feat(web): header pill showing PhotoPrism indexer status

Subscribes to PhotoPrism's /api/v1/ws channel on login and surfaces
index.indexing / index.updating / index.completed events as a small
status pill in the header (next to the AnimatedMule wordmark).

- Shows "Indexing" + the current filename (basename, monospace) during
  the scan pass, "Finalizing — <step>" during faces/counts/folders/
  purge/moments, and "Indexed in Ns" for ~4s after completion before
  fading.
- Per-file events arrive many per second on large libraries — throttled
  to 150 ms with a trailing-edge update so the pill stays calm and
  always lands on the most recent filename. Step and completion events
  bypass the throttle.
- Filename slot is fixed at 24ch so the pill width stays constant
  through a run (no horizontal jitter as filenames change length); the
  full path is exposed via the parent's `title` for hover.
- WS reconnect uses exponential backoff capped at 30 s, and the store
  tears down cleanly on logout so we don't leak sockets across
  identities.

Defensive parsing throughout: PhotoPrism's WS protocol isn't a stable
contract, so unknown event shapes are ignored rather than thrown —
worst-case the pill stays idle.

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

web/src/routes/+layout.svelte

@@ -14,6 +14,8 @@
 	import { resizable } from '$lib/actions/resizable';
 	import { queryClient } from '$lib/queryClient';
 	import { preview } from '$lib/stores/preview.svelte';
+	import { startIndexerWatch, stopIndexerWatch } from '$lib/stores/indexer.svelte';
+	import IndexerStatusPill from '$lib/components/layout/IndexerStatusPill.svelte';
 	import LeftSidebar from '$lib/components/layout/LeftSidebar.svelte';
 	import AnimatedMule from '$lib/components/mule/AnimatedMule.svelte';
 
@@ -44,6 +46,16 @@
 		}
 	});
 
+	// Indexer status feed. The store opens a WS to PhotoPrism's /api/v1/ws
+	// channel once we're signed in and tears it down on logout. Kept here
+	// (not in the store's top-level) so SvelteKit's SSR pass never touches
+	// `WebSocket` and so logout can short-circuit reconnect attempts.
+	$effect(() => {
+		if (!browser || !bootstrapped) return;
+		if (isAuthenticated()) startIndexerWatch();
+		else stopIndexerWatch();
+	});
+
 	// PreviewOverlay is the full-screen lightbox — keyboard nav, map
 	// pane, exif sidebar. Users who never click into a photo never need
 	// it, so we lazy-import the first time `preview.uid` flips non-null
@@ -75,7 +87,9 @@
 		     region inside each page scrolls. The mule header, toolbar, and
 		     sidebars stay fixed regardless of how far you scroll the grid. -->
 		<div class="flex h-screen flex-col overflow-hidden">
-			<AnimatedMule />
+			<AnimatedMule>
+				<IndexerStatusPill />
+			</AnimatedMule>
 			<div class="flex min-h-0 flex-1">
 				{#if !view.leftSidebarCollapsed}
 					<aside