feat: the Wanted view becomes Collection, shaped like Lidarr: an artist catalogue first, the state sections down a left rail (M502 #5577)

The section opens on a catalogue of every artist on the list, A–Z with a
letter rail, each card showing how many of their albums are held. An artist
opens on their page: every album of theirs, held or not, with its status,
search, releases and tracks. Wanted, Missing files, Activity, Following and
Blocked sit down a left rail as the sections that show state; Held is gone,
the catalogue shows it. The section moves from /wanted to /collection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/routes/collection/+layout.ts

@@ -0,0 +1,13 @@
+import { redirect } from '@sveltejs/kit';
+import { user } from '#lib/auth/store.svelte.js';
+import type { LayoutLoad } from './$types';
+
+// Hard route gate: the Wanted view is an admin's (M502). Runs before the
+// layout renders; auth is bootstrapped by the root +layout.ts, so user.value is
+// either a settled User object or null.
+export const load: LayoutLoad = () => {
+  if (!user.value || !user.value.is_admin) {
+    throw redirect(302, '/');
+  }
+  return {};
+};