feat(video): add video upload with remux/transcode playback

Add video as a media kind in photos: streaming upload with per-kind
limits, ffprobe metadata, poster frame reusing the image variant
pipeline, and a playback object (remux when web-compatible, else
h264/yuv420p/aac transcode). Video jobs run on a separate pool with a
long lease. Frontend gains a video viewer, grid badge/duration and
video upload.

frontend/src/lib/components/PhotoGrid.svelte

@@ -50,6 +50,14 @@
 
 	const isSelected = (id: string) => selectedIds.includes(id);
 	const isCursor = (i: number) => cursorIndex === i;
+
+	function formatDuration(ms?: number): string {
+		if (!ms || ms <= 0) return '';
+		const total = Math.round(ms / 1000);
+		const m = Math.floor(total / 60);
+		const s = total % 60;
+		return `${m}:${String(s).padStart(2, '0')}`;
+	}
 	const tabIndexFor = (i: number) =>
 		cursorIndex == null ? (i === 0 ? 0 : -1) : isCursor(i) ? 0 : -1;
 
@@ -117,6 +125,21 @@
 							360
 						</span>
 					{/if}
+					{#if photo.kind === 'video'}
+						<span
+							class="absolute top-1 left-1 inline-flex items-center justify-center rounded bg-black/60 p-1 text-white"
+							aria-label="Видео"
+						>
+							<Icon name="play_arrow" class="size-4" />
+						</span>
+						{#if formatDuration(photo.duration_ms)}
+							<span
+								class="absolute bottom-1 left-1 rounded bg-black/70 px-1.5 py-0.5 text-[10px] font-medium text-white"
+							>
+								{formatDuration(photo.duration_ms)}
+							</span>
+						{/if}
+					{/if}
 					<span
 						class="bg-bg/70 text-text absolute right-1 bottom-1 flex items-center gap-1.5 rounded px-1.5 py-0.5 text-xs"
 					>