feat(frontend): viewer fullscreen chrome and pointer-accurate zoom

- fullscreen: auto-hide top toolbar and filmstrip, revealed at top/bottom
  screen edge and hidden 1s after the cursor leaves
- arrows < >: edge-reveal in both normal and fullscreen; hide 300ms after
  leaving; hidden while zoomed
- zoom: wheel zooms only (no scroll, overscroll contained), anchored to the
  pointer, capped at 200%; Space toggles 100%/fit; pan via drag/scroll

frontend/src/lib/components/Viewer.svelte

@@ -31,17 +31,29 @@
 
 	const current = $derived(photos[index]);
 
-	const MIN_ZOOM = 0.1;
+	const MAX_ZOOM = 2;
-	const MAX_ZOOM = 8;
 
 	let viewerEl: HTMLDivElement | undefined = $state();
 	let scroller: HTMLDivElement | undefined = $state();
 	let imgEl: HTMLImageElement | undefined = $state();
+	let topEl: HTMLDivElement | undefined = $state();
+	let bottomEl: HTMLDivElement | undefined = $state();
 
 	let isFullscreen = $state(false);
 	let zoomed = $state(false);
 	let scale = $state(1);
 
+	let showTop = $state(false);
+	let showBottom = $state(false);
+	let showLeft = $state(false);
+	let showRight = $state(false);
+
+	const EDGE = 8;
+	let hideTopTimer: ReturnType<typeof setTimeout> | undefined;
+	let hideBottomTimer: ReturnType<typeof setTimeout> | undefined;
+	let hideLeftTimer: ReturnType<typeof setTimeout> | undefined;
+	let hideRightTimer: ReturnType<typeof setTimeout> | undefined;
+
 	let dragging = false;
 	let startX = 0;
 	let startY = 0;
@@ -68,13 +80,135 @@
 	});
 
 	$effect(() => {
-		const onFs = () => (isFullscreen = !!viewerEl && document.fullscreenElement === viewerEl);
+		const onFs = () => {
+			isFullscreen = !!viewerEl && document.fullscreenElement === viewerEl;
+			resetBars();
+		};
 		document.addEventListener('fullscreenchange', onFs);
-		return () => document.removeEventListener('fullscreenchange', onFs);
+		return () => {
+			document.removeEventListener('fullscreenchange', onFs);
+			clearTimeout(hideTopTimer);
+			clearTimeout(hideBottomTimer);
+			clearTimeout(hideLeftTimer);
+			clearTimeout(hideRightTimer);
+		};
 	});
 
+	const topClass = $derived(
+		isFullscreen
+			? `border-border bg-chrome absolute inset-x-0 top-0 z-30 flex items-center justify-between gap-2 border-b px-3 py-2 transition-transform duration-200 ${showTop ? 'translate-y-0' : '-translate-y-full'}`
+			: 'border-border bg-chrome flex shrink-0 items-center justify-between gap-2 border-b px-3 py-2'
+	);
+	const bottomClass = $derived(
+		isFullscreen
+			? `border-border bg-chrome absolute inset-x-0 bottom-0 z-30 flex gap-2 overflow-x-auto border-t p-2 transition-transform duration-200 ${showBottom ? 'translate-y-0' : 'translate-y-full'}`
+			: 'border-border bg-chrome flex shrink-0 gap-2 overflow-x-auto border-t p-2'
+	);
+	const arrowPos =
+		'absolute top-1/2 z-20 inline-flex -translate-y-1/2 items-center justify-center rounded-full bg-black/40 p-1.5 text-text backdrop-blur transition-opacity duration-200 hover:text-white';
+	const arrowVisibility = (shown: boolean, disabled: boolean, isZoomed: boolean) =>
+		isZoomed || !shown ? 'pointer-events-none opacity-0' : disabled ? 'opacity-40' : 'opacity-100';
+	const leftDisabled = $derived(index === 0 || zoomed);
+	const rightDisabled = $derived(index === photos.length - 1 || zoomed);
+	const leftBtnClass = $derived(
+		`${arrowPos} left-2 ${arrowVisibility(showLeft, leftDisabled, zoomed)}`
+	);
+	const rightBtnClass = $derived(
+		`${arrowPos} right-2 ${arrowVisibility(showRight, rightDisabled, zoomed)}`
+	);
+
+	function resetBars() {
+		clearTimeout(hideTopTimer);
+		clearTimeout(hideBottomTimer);
+		clearTimeout(hideLeftTimer);
+		clearTimeout(hideRightTimer);
+		hideTopTimer = undefined;
+		hideBottomTimer = undefined;
+		hideLeftTimer = undefined;
+		hideRightTimer = undefined;
+		showTop = false;
+		showBottom = false;
+		showLeft = false;
+		showRight = false;
+	}
+
+	function inRect(el: HTMLElement | undefined, x: number, y: number): boolean {
+		if (!el) return false;
+		const r = el.getBoundingClientRect();
+		return x >= r.left && x <= r.right && y >= r.top && y <= r.bottom;
+	}
+
+	function scheduleTop(shouldShow: boolean) {
+		if (shouldShow) {
+			clearTimeout(hideTopTimer);
+			hideTopTimer = undefined;
+			showTop = true;
+		} else if (showTop && !hideTopTimer) {
+			hideTopTimer = setTimeout(() => {
+				showTop = false;
+				hideTopTimer = undefined;
+			}, 1000);
+		}
+	}
+
+	function scheduleBottom(shouldShow: boolean) {
+		if (shouldShow) {
+			clearTimeout(hideBottomTimer);
+			hideBottomTimer = undefined;
+			showBottom = true;
+		} else if (showBottom && !hideBottomTimer) {
+			hideBottomTimer = setTimeout(() => {
+				showBottom = false;
+				hideBottomTimer = undefined;
+			}, 1000);
+		}
+	}
+
+	function scheduleLeft(shouldShow: boolean) {
+		if (shouldShow) {
+			clearTimeout(hideLeftTimer);
+			hideLeftTimer = undefined;
+			showLeft = true;
+		} else if (showLeft && !hideLeftTimer) {
+			hideLeftTimer = setTimeout(() => {
+				showLeft = false;
+				hideLeftTimer = undefined;
+			}, 300);
+		}
+	}
+
+	function scheduleRight(shouldShow: boolean) {
+		if (shouldShow) {
+			clearTimeout(hideRightTimer);
+			hideRightTimer = undefined;
+			showRight = true;
+		} else if (showRight && !hideRightTimer) {
+			hideRightTimer = setTimeout(() => {
+				showRight = false;
+				hideRightTimer = undefined;
+			}, 300);
+		}
+	}
+
+	function onWinMouseMove(e: MouseEvent) {
+		const r = viewerEl?.getBoundingClientRect();
+		if (r) {
+			const zoneX = r.width / 6;
+			scheduleLeft(!zoomed && e.clientX <= r.left + zoneX);
+			scheduleRight(!zoomed && e.clientX >= r.right - zoneX);
+		}
+		if (!isFullscreen) return;
+		const nearTop = e.clientY <= EDGE;
+		const nearBottom = e.clientY >= window.innerHeight - EDGE;
+		scheduleTop(nearTop || inRect(topEl, e.clientX, e.clientY));
+		scheduleBottom(nearBottom || inRect(bottomEl, e.clientX, e.clientY));
+	}
+
 	function baseWidth(): number {
-		return fresh?.width || current?.width || imgEl?.naturalWidth || 0;
+		return imgEl?.naturalWidth || fresh?.width || current?.width || 0;
+	}
+	function baseHeight(): number {
+		return imgEl?.naturalHeight || fresh?.height || current?.height || 0;
 	}
 
 	function prev() {
@@ -85,42 +219,52 @@
 	}
 
 	function toggleActual() {
-		if (zoomed && scale === 1) {
+		const atHundred = zoomed && Math.abs(scale - 1) < 0.01;
+		if (atHundred) {
 			zoomed = false;
 			scale = 1;
+			if (scroller) {
+				scroller.scrollLeft = 0;
+				scroller.scrollTop = 0;
+			}
 		} else {
 			zoomed = true;
 			scale = 1;
+			tick().then(() => {
+				if (!scroller) return;
+				scroller.scrollLeft = (scroller.scrollWidth - scroller.clientWidth) / 2;
+				scroller.scrollTop = (scroller.scrollHeight - scroller.clientHeight) / 2;
+			});
 		}
 	}
 
 	function onWheel(ev: WheelEvent) {
-		if (!current || !scroller) return;
+		if (!current || !scroller || !imgEl) return;
 		ev.preventDefault();
-		const factor = ev.deltaY < 0 ? 1.15 : 1 / 1.15;
+		ev.stopPropagation();
-		const newScale = Math.min(MAX_ZOOM, Math.max(MIN_ZOOM, scale * factor));
-		if (newScale === scale) return;
 
-		const rect = scroller.getBoundingClientRect();
+		const natW = baseWidth();
-		const ox = ev.clientX - rect.left;
+		const natH = baseHeight();
-		const oy = ev.clientY - rect.top;
+		if (!natW || !natH) return;
-		const wasFit = !zoomed;
+
-		const oldScale = scale;
+		const factor = ev.deltaY < 0 ? 1.15 : 1 / 1.15;
+		const fitScale = Math.min(scroller.clientWidth / natW, scroller.clientHeight / natH, 1);
+		const curScale = zoomed ? scale : fitScale;
+		const newScale = Math.min(MAX_ZOOM, Math.max(fitScale, curScale * factor));
+		if (Math.abs(newScale - curScale) < 1e-4) return;
+
+		const r = imgEl.getBoundingClientRect();
+		const fx = (ev.clientX - r.left) / r.width;
+		const fy = (ev.clientY - r.top) / r.height;
 
 		zoomed = true;
 		scale = newScale;
 
 		tick().then(() => {
 			if (!scroller) return;
-			if (wasFit) {
+			const sr = scroller.getBoundingClientRect();
-				scroller.scrollLeft = scroller.scrollWidth / 2 - ox;
+			scroller.scrollLeft = fx * natW * newScale - (ev.clientX - sr.left);
-				scroller.scrollTop = scroller.scrollHeight / 2 - oy;
+			scroller.scrollTop = fy * natH * newScale - (ev.clientY - sr.top);
-			} else {
-				const nx = (scroller.scrollLeft + ox) / oldScale;
-				const ny = (scroller.scrollTop + oy) / oldScale;
-				scroller.scrollLeft = nx * newScale - ox;
-				scroller.scrollTop = ny * newScale - oy;
-			}
 		});
 	}
 
@@ -207,10 +351,10 @@
 		'border-border text-danger hover:bg-bg-muted inline-flex items-center gap-1.5 rounded-lg border px-3 py-1.5 text-sm';
 </script>
 
-<svelte:window onkeydown={onKey} />
+<svelte:window onkeydown={onKey} onmousemove={onWinMouseMove} />
 
-<div bind:this={viewerEl} class="bg-canvas flex h-full flex-col">
+<div bind:this={viewerEl} class="bg-canvas relative flex h-full flex-col overflow-hidden">
-	<div class="border-border bg-chrome flex shrink-0 items-center justify-between gap-2 border-b px-3 py-2">
+	<div bind:this={topEl} class={topClass}>
 		<div class="flex items-center gap-2">
 			<button type="button" class={btn} aria-label="Назад" title="Назад" onclick={onClose}>
 				<Icon name="arrow_back" />
@@ -222,7 +366,9 @@
 				type="button"
 				class={btn}
 				aria-label={isFullscreen ? 'Выйти из полноэкранного просмотра' : 'Полноэкранный просмотр'}
-				title={isFullscreen ? 'Выйти из полноэкранного просмотра (f)' : 'Полноэкранный просмотр (f)'}
+				title={isFullscreen
+					? 'Выйти из полноэкранного просмотра (f)'
+					: 'Полноэкранный просмотр (f)'}
 				aria-pressed={isFullscreen}
 				onclick={toggleViewerFullscreen}
 			>
@@ -259,21 +405,23 @@
 		</div>
 	</div>
 
-	<div class="flex min-h-0 flex-1 items-stretch">
+	<div class="relative flex min-h-0 flex-1 items-stretch">
 		<button
 			type="button"
-			class="text-text-muted hover:text-text inline-flex shrink-0 items-center self-center px-1 disabled:opacity-30"
+			class={leftBtnClass}
 			aria-label="Предыдущее фото"
 			title="Предыдущее фото"
 			onclick={prev}
-			disabled={index === 0 || zoomed}
+			disabled={leftDisabled}
 		>
 			<Icon name="chevron_left" class="size-8" />
 		</button>
 
 		<div
 			bind:this={scroller}
-			class="bg-canvas flex min-h-0 flex-1 {zoomed ? 'cursor-grab overflow-auto' : 'overflow-hidden'}"
+			class="bg-canvas flex min-h-0 flex-1 overscroll-contain {zoomed
+				? 'cursor-grab overflow-auto'
+				: 'overflow-hidden'}"
 			role="group"
 			aria-label="Просмотр фото"
 			onpointerdown={onPointerDown}
@@ -294,7 +442,7 @@
 					draggable="false"
 					style={zoomed ? `width: ${baseWidth() * scale}px; height: auto;` : ''}
 					class="m-auto block {zoomed
-						? 'max-w-none select-none'
+						? 'max-w-none shrink-0 select-none'
 						: 'max-h-full max-w-full object-contain'}"
 				/>
 			{/if}
@@ -302,20 +450,17 @@
 
 		<button
 			type="button"
-			class="text-text-muted hover:text-text inline-flex shrink-0 items-center self-center px-1 disabled:opacity-30"
+			class={rightBtnClass}
 			aria-label="Следующее фото"
 			title="Следующее фото"
 			onclick={next}
-			disabled={index === photos.length - 1 || zoomed}
+			disabled={rightDisabled}
 		>
 			<Icon name="chevron_right" class="size-8" />
 		</button>
 	</div>
 
-	<div
+	<div bind:this={bottomEl} class={bottomClass} aria-label="Лента миниатюр">
-		class="border-border flex shrink-0 gap-2 overflow-x-auto border-t p-2"
-		aria-label="Лента миниатюр"
-	>
 		{#each photos as photo, i (photo.id)}
 			<button
 				type="button"