feat(frontend): photo viewer fullscreen and zoom

- fullscreen toggle button + "f" hotkey (both layouts)
- wheel zoom anchored to cursor; Space toggles 100% (1:1)
- pan when zoomed via drag/scrollbars; reset zoom on photo change
- hotkeys ignored while typing in inputs

frontend/src/lib/components/Viewer.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+	import { tick } from 'svelte';
 	import { api } from '$lib/api';
 	import Icon from './Icon.svelte';
 	import type { Photo } from '$lib/types';
@@ -30,15 +31,52 @@
 
 	const current = $derived(photos[index]);
 
+	const MIN_ZOOM = 0.1;
+	const MAX_ZOOM = 8;
+
+	let viewerEl: HTMLDivElement | undefined = $state();
+	let scroller: HTMLDivElement | undefined = $state();
+	let imgEl: HTMLImageElement | undefined = $state();
+
+	let isFullscreen = $state(false);
+	let zoomed = $state(false);
+	let scale = $state(1);
+
+	let dragging = false;
+	let startX = 0;
+	let startY = 0;
+	let startL = 0;
+	let startT = 0;
+
 	$effect(() => {
 		const id = current?.id;
 		fresh = null;
+		zoomed = false;
+		scale = 1;
 		if (!id) return;
 		api<{ photo: Photo }>(`/photos/${id}`)
 			.then((data) => (fresh = data.photo))
 			.catch(() => {});
 	});
 
+	$effect(() => {
+		const el = scroller;
+		if (!el) return;
+		const handler = (e: WheelEvent) => onWheel(e);
+		el.addEventListener('wheel', handler, { passive: false });
+		return () => el.removeEventListener('wheel', handler);
+	});
+
+	$effect(() => {
+		const onFs = () => (isFullscreen = !!viewerEl && document.fullscreenElement === viewerEl);
+		document.addEventListener('fullscreenchange', onFs);
+		return () => document.removeEventListener('fullscreenchange', onFs);
+	});
+
+	function baseWidth(): number {
+		return fresh?.width || current?.width || imgEl?.naturalWidth || 0;
+	}
+
 	function prev() {
 		if (index > 0) onIndexChange(index - 1);
 	}
@@ -46,9 +84,110 @@
 		if (index < photos.length - 1) onIndexChange(index + 1);
 	}
 
+	function toggleActual() {
+		if (zoomed && scale === 1) {
+			zoomed = false;
+			scale = 1;
+		} else {
+			zoomed = true;
+			scale = 1;
+		}
+	}
+
+	function onWheel(ev: WheelEvent) {
+		if (!current || !scroller) return;
+		ev.preventDefault();
+		const factor = ev.deltaY < 0 ? 1.15 : 1 / 1.15;
+		const newScale = Math.min(MAX_ZOOM, Math.max(MIN_ZOOM, scale * factor));
+		if (newScale === scale) return;
+
+		const rect = scroller.getBoundingClientRect();
+		const ox = ev.clientX - rect.left;
+		const oy = ev.clientY - rect.top;
+		const wasFit = !zoomed;
+		const oldScale = scale;
+
+		zoomed = true;
+		scale = newScale;
+
+		tick().then(() => {
+			if (!scroller) return;
+			if (wasFit) {
+				scroller.scrollLeft = scroller.scrollWidth / 2 - ox;
+				scroller.scrollTop = scroller.scrollHeight / 2 - oy;
+			} else {
+				const nx = (scroller.scrollLeft + ox) / oldScale;
+				const ny = (scroller.scrollTop + oy) / oldScale;
+				scroller.scrollLeft = nx * newScale - ox;
+				scroller.scrollTop = ny * newScale - oy;
+			}
+		});
+	}
+
+	function onPointerDown(ev: PointerEvent) {
+		if (!zoomed || !scroller || ev.pointerType !== 'mouse') return;
+		dragging = true;
+		startX = ev.clientX;
+		startY = ev.clientY;
+		startL = scroller.scrollLeft;
+		startT = scroller.scrollTop;
+		try {
+			scroller.setPointerCapture(ev.pointerId);
+		} catch {
+			/* ignore */
+		}
+	}
+	function onPointerMove(ev: PointerEvent) {
+		if (!dragging || !scroller) return;
+		ev.preventDefault();
+		scroller.scrollLeft = startL - (ev.clientX - startX);
+		scroller.scrollTop = startT - (ev.clientY - startY);
+	}
+	function onPointerUp(ev: PointerEvent) {
+		if (!dragging) return;
+		dragging = false;
+		try {
+			scroller?.releasePointerCapture(ev.pointerId);
+		} catch {
+			/* ignore */
+		}
+	}
+
+	async function toggleViewerFullscreen() {
+		if (!viewerEl) return;
+		try {
+			if (document.fullscreenElement) await document.exitFullscreen();
+			else await viewerEl.requestFullscreen();
+		} catch {
+			/* недоступно */
+		}
+	}
+
+	function isTyping(): boolean {
+		const el = document.activeElement as HTMLElement | null;
+		if (!el) return false;
+		const tag = el.tagName;
+		return tag === 'INPUT' || tag === 'TEXTAREA' || tag === 'SELECT' || el.isContentEditable;
+	}
+
 	function onKey(ev: KeyboardEvent) {
-		if (ev.key === 'Escape') onClose();
+		if (isTyping()) return;
-		else if (ev.key === 'ArrowLeft') prev();
+		if (ev.key === 'Escape') {
+			if (!document.fullscreenElement) onClose();
+			return;
+		}
+		if (ev.code === 'Space') {
+			ev.preventDefault();
+			toggleActual();
+			return;
+		}
+		if (ev.key === 'f' || ev.key === 'F' || ev.key === 'а' || ev.key === 'А') {
+			ev.preventDefault();
+			toggleViewerFullscreen();
+			return;
+		}
+		if (zoomed) return;
+		if (ev.key === 'ArrowLeft') prev();
 		else if (ev.key === 'ArrowRight') next();
 	}
 
@@ -56,6 +195,7 @@
 		touchX = ev.changedTouches[0].clientX;
 	}
 	function onTouchEnd(ev: TouchEvent) {
+		if (zoomed) return;
 		const dx = ev.changedTouches[0].clientX - touchX;
 		if (dx > 50) prev();
 		else if (dx < -50) next();
@@ -69,8 +209,8 @@
 
 <svelte:window onkeydown={onKey} />
 
-<div class="flex h-full flex-col">
+<div bind:this={viewerEl} class="bg-canvas flex h-full flex-col">
-	<div class="border-border flex shrink-0 items-center justify-between gap-2 border-b px-3 py-2">
+	<div class="border-border bg-chrome flex shrink-0 items-center justify-between gap-2 border-b px-3 py-2">
 		<div class="flex items-center gap-2">
 			<button type="button" class={btn} aria-label="Назад" title="Назад" onclick={onClose}>
 				<Icon name="arrow_back" />
@@ -78,6 +218,16 @@
 			<span class="text-text-muted text-sm">{index + 1} / {photos.length}</span>
 		</div>
 		<div class="flex items-center gap-2">
+			<button
+				type="button"
+				class={btn}
+				aria-label={isFullscreen ? 'Выйти из полноэкранного просмотра' : 'Полноэкранный просмотр'}
+				title={isFullscreen ? 'Выйти из полноэкранного просмотра (f)' : 'Полноэкранный просмотр (f)'}
+				aria-pressed={isFullscreen}
+				onclick={toggleViewerFullscreen}
+			>
+				<Icon name={isFullscreen ? 'fullscreen_exit' : 'fullscreen'} />
+			</button>
 			{#if canEdit}
 				<button
 					type="button"
@@ -109,46 +259,63 @@
 		</div>
 	</div>
 
-	<div
+	<div class="flex min-h-0 flex-1 items-stretch">
-		class="bg-canvas flex min-h-0 flex-1 items-center justify-center overflow-hidden px-2 py-2"
-		role="group"
-		aria-label="Просмотр фото"
-		ontouchstart={onTouchStart}
-		ontouchend={onTouchEnd}
-	>
 		<button
 			type="button"
-			class="text-text-muted hover:text-text inline-flex items-center px-1 disabled:opacity-30"
+			class="text-text-muted hover:text-text inline-flex shrink-0 items-center self-center px-1 disabled:opacity-30"
 			aria-label="Предыдущее фото"
 			title="Предыдущее фото"
 			onclick={prev}
-			disabled={index === 0}
+			disabled={index === 0 || zoomed}
 		>
 			<Icon name="chevron_left" class="size-8" />
 		</button>
-		{#if current}
+
-			<img
+		<div
-				src={fresh?.preview_url ??
+			bind:this={scroller}
-					fresh?.original_url ??
+			class="bg-canvas flex min-h-0 flex-1 {zoomed ? 'cursor-grab overflow-auto' : 'overflow-hidden'}"
-					current.preview_url ??
+			role="group"
-					current.original_url}
+			aria-label="Просмотр фото"
-				alt={current.original_filename}
+			onpointerdown={onPointerDown}
-				class="max-h-full max-w-full rounded-lg object-contain"
+			onpointermove={onPointerMove}
-			/>
+			onpointerup={onPointerUp}
-		{/if}
+			onpointercancel={onPointerUp}
+			ontouchstart={onTouchStart}
+			ontouchend={onTouchEnd}
+		>
+			{#if current}
+				<img
+					bind:this={imgEl}
+					src={fresh?.preview_url ??
+						fresh?.original_url ??
+						current.preview_url ??
+						current.original_url}
+					alt={current.original_filename}
+					draggable="false"
+					style={zoomed ? `width: ${baseWidth() * scale}px; height: auto;` : ''}
+					class="m-auto block {zoomed
+						? 'max-w-none select-none'
+						: 'max-h-full max-w-full object-contain'}"
+				/>
+			{/if}
+		</div>
+
 		<button
 			type="button"
-			class="text-text-muted hover:text-text inline-flex items-center px-1 disabled:opacity-30"
+			class="text-text-muted hover:text-text inline-flex shrink-0 items-center self-center px-1 disabled:opacity-30"
 			aria-label="Следующее фото"
 			title="Следующее фото"
 			onclick={next}
-			disabled={index === photos.length - 1}
+			disabled={index === photos.length - 1 || zoomed}
 		>
 			<Icon name="chevron_right" class="size-8" />
 		</button>
 	</div>
 
-	<div class="border-border flex shrink-0 gap-2 overflow-x-auto border-t p-2" aria-label="Лента миниатюр">
+	<div
+		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"