preview: full-screen modal replaces inline split + tags route reorg

The old SplitGrid + InlinePreview pane is replaced by a full-screen
PreviewModal mounted once at the layout root. Open via Space on the
focused tile or double-click; close on Esc (or X / Space again).
Inside, PreviewPane renders the focused photo, RightSidebar carries
the metadata, BulkActionBar reuses the existing per-photo actions,
and PreviewCarousel windows ±50 thumbs around the focused index.

Selection contract matches the grid: plain click reduces, shift
extends the range, ⌘/Ctrl toggles, plain arrow drops the multi-
selection, shift-arrow extends. New clearBulkToFirst() helper makes
Esc / Clear collapse a bulk back to single-focus on its first member
before the next press fully dismisses (modal closes, grid clears
focus).

Tags route reorganised into /tags/[category]/[[value]] with its own
+layout and TagsBrowserSidebar; the old monolithic /tags/+page is
trimmed to a legacy redirect.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/components/preview/PreviewPane.svelte

@@ -0,0 +1,112 @@
+<!--
+	Inner preview surface used by the full-screen PreviewModal and the
+	shareable /photo/[uid] deep-link route. Renders the focused photo or
+	video, with optional prev/next chevrons that walk `order` via
+	setFocused.
+
+	Video mounting is debounced 250 ms so arrow-skim across a stretch of
+	video tiles doesn't open (and immediately cancel) range requests we'd
+	throw away. Until the timer fires, the poster image stands in.
+-->
+<script lang="ts">
+	import { createQuery } from '@tanstack/svelte-query';
+	import { getPhoto } from '$lib/services/photoprism';
+	import { thumbUrl, videoUrl } from '$lib/stores/session.svelte';
+	import { setAnchor, setFocused } from '$lib/stores/selection.svelte';
+	import VideoPlayer from '$lib/components/preview/VideoPlayer.svelte';
+	import { isVideo, primaryFile, videoFile, type PpPhoto } from '$lib/types/photoprism';
+
+	interface Props {
+		uid: string | null;
+		order: string[];
+		/** Hide the floating prev/next chevrons (callers that wrap their
+		 *  own nav can disable to avoid duplication). */
+		showChevrons?: boolean;
+	}
+	let { uid, order, showChevrons = true }: Props = $props();
+
+	const photoQuery = createQuery<PpPhoto>(() => ({
+		queryKey: ['photo', uid ?? ''],
+		queryFn: () => getPhoto(uid as string),
+		enabled: Boolean(uid)
+	}));
+
+	const currentIndex = $derived(uid ? order.indexOf(uid) : -1);
+
+	const VIDEO_LOAD_DELAY_MS = 250;
+	let armedUid = $state<string | null>(null);
+
+	$effect(() => {
+		const target = uid;
+		if (!target) {
+			armedUid = null;
+			return;
+		}
+		const t = setTimeout(() => {
+			armedUid = target;
+		}, VIDEO_LOAD_DELAY_MS);
+		return () => clearTimeout(t);
+	});
+
+	function focusAt(i: number) {
+		const next = order[i];
+		if (!next) return;
+		setFocused(next);
+		setAnchor(next);
+	}
+</script>
+
+<div class="relative flex h-full w-full items-center justify-center bg-black/40 p-4">
+	{#if uid === null}
+		<p class="text-sm text-muted-foreground">Select a photo to preview.</p>
+	{:else if photoQuery.isPending}
+		<p class="text-sm text-muted-foreground">Loading…</p>
+	{:else if photoQuery.isError}
+		<p class="text-sm text-destructive">Failed to load photo.</p>
+	{:else if photoQuery.data}
+		{@const pf = primaryFile(photoQuery.data)}
+		{#if showChevrons && currentIndex > 0}
+			<button
+				class="absolute left-2 top-1/2 z-10 -translate-y-1/2 rounded-full bg-background/80 px-3 py-2 text-lg hover:bg-background"
+				onclick={() => focusAt(currentIndex - 1)}
+				aria-label="Previous photo"
+			>
+				‹
+			</button>
+		{/if}
+		{#if showChevrons && currentIndex >= 0 && currentIndex < order.length - 1}
+			<button
+				class="absolute right-2 top-1/2 z-10 -translate-y-1/2 rounded-full bg-background/80 px-3 py-2 text-lg hover:bg-background"
+				onclick={() => focusAt(currentIndex + 1)}
+				aria-label="Next photo"
+			>
+				›
+			</button>
+		{/if}
+
+		{#if isVideo(photoQuery.data)}
+			{@const vf = videoFile(photoQuery.data)}
+			{#if armedUid === uid}
+				{#key vf.Hash}
+					<VideoPlayer
+						src={videoUrl(vf.Hash)}
+						poster={thumbUrl(pf.Hash, 'fit_1280')}
+						title={photoQuery.data.OriginalName ?? pf.Name ?? ''}
+					/>
+				{/key}
+			{:else}
+				<img
+					src={thumbUrl(pf.Hash, 'fit_1280')}
+					alt={photoQuery.data.OriginalName ?? pf.Name ?? 'Video'}
+					class="max-h-full max-w-full rounded-md object-contain shadow-2xl"
+				/>
+			{/if}
+		{:else}
+			<img
+				src={thumbUrl(pf.Hash, 'fit_1280')}
+				alt={photoQuery.data.OriginalName ?? pf.Name ?? 'Photo'}
+				class="max-h-full max-w-full rounded-md object-contain shadow-2xl"
+			/>
+		{/if}
+	{/if}
+</div>