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/routes/+page.svelte

@@ -35,6 +35,7 @@
     setOrder,
   } from "$lib/stores/selection.svelte";
   import {
+    openPreview,
     setRightSidebarWidth,
     setThumbnailSize,
     THUMBNAIL_SIZE_LABELS,
@@ -51,11 +52,9 @@
   } from "$lib/actions/visibleRange";
   import BulkActionBar from "$lib/components/timeline/BulkActionBar.svelte";
   import BulkMetadataSidebar from "$lib/components/sidebar/BulkMetadataSidebar.svelte";
-  import InlinePreview from "$lib/components/preview/InlinePreview.svelte";
   import PhotoTile from "$lib/components/timeline/PhotoTile.svelte";
   import RightSidebar from "$lib/components/sidebar/RightSidebar.svelte";
   import SkeletonGrid from "$lib/components/timeline/SkeletonGrid.svelte";
-  import SplitGrid from "$lib/components/preview/SplitGrid.svelte";
   import Toolbar from "$lib/components/layout/Toolbar.svelte";
   import { type PpPhoto } from "$lib/types/photoprism";
 
@@ -668,6 +667,7 @@
     selection.ids.add(uid);
     setFocused(uid);
     setAnchor(uid);
+    openPreview();
   }
 
   // Scroll root for the infinite-scroll IntersectionObserver. Bound by
@@ -815,11 +815,6 @@
 		sibling at row level and stays full height when the bar appears.
 	-->
   <div class="flex min-w-0 flex-1 flex-col overflow-hidden">
-    <SplitGrid>
-      {#snippet preview()}
-        <InlinePreview uid={selection.focused} order={selection.order} />
-      {/snippet}
-      {#snippet grid()}
         <main
           bind:this={scrollRoot}
           class="flex-1 overflow-y-auto outline-none focus:outline-none"
@@ -932,8 +927,6 @@
             {/if}
           </div>
         </main>
-      {/snippet}
-    </SplitGrid>
     <BulkActionBar />
   </div>