feat: add visual admin panel with page builder and settings editor

- Add /admin route with password-protected visual page builder
- Page Builder: manage hero images, standalone albums, subpages, and sections
- Album Picker: browse all shared Immich albums with search and filtering
- Settings Editor: theme, grid, footer, legal, SEO configuration
- YAML service with atomic writes and automatic backups (content/.backups/)
- HMAC-signed admin sessions (24h expiry, HttpOnly cookies)
- API endpoints: /api/admin/{auth,gallery,settings,albums,reload}
- Enable with ADMIN_PASSWORD env var; disabled by default
- invalidateConfigCache() export for hot-reload after saves

app/api/admin/albums/route.ts

@@ -0,0 +1,67 @@
+import { NextResponse } from 'next/server';
+import { isAdminAuthenticated, isAdminEnabled } from '@/lib/admin/auth';
+import { getConfig } from '@/lib/config';
+
+interface ImmichAlbumSummary {
+  id: string;
+  albumName: string;
+  description: string;
+  albumThumbnailAssetId: string | null;
+  assetCount: number;
+  createdAt: string;
+  updatedAt: string;
+}
+
+/** GET: List ALL shared Immich albums (not just allowlisted ones). */
+export async function GET() {
+  if (!isAdminEnabled()) {
+    return NextResponse.json({ error: 'Admin not enabled' }, { status: 403 });
+  }
+  if (!(await isAdminAuthenticated())) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+  }
+
+  const config = getConfig();
+  if (config.needsSetup) {
+    return NextResponse.json({ error: 'Immich not configured' }, { status: 503 });
+  }
+
+  try {
+    const res = await fetch(`${config.immich.apiUrl}/albums?shared=true`, {
+      headers: {
+        'x-api-key': config.immich.apiKey,
+        Accept: 'application/json',
+      },
+    });
+
+    if (!res.ok) {
+      return NextResponse.json({ error: `Immich API returned ${res.status}` }, { status: 502 });
+    }
+
+    const albums = (await res.json()) as ImmichAlbumSummary[];
+
+    // Mark which albums are already configured
+    const configuredIds = new Set(config.albums);
+    const enriched = albums.map((album) => ({
+      id: album.id,
+      albumName: album.albumName,
+      description: album.description || '',
+      thumbnailAssetId: album.albumThumbnailAssetId,
+      assetCount: album.assetCount,
+      createdAt: album.createdAt,
+      updatedAt: album.updatedAt,
+      isConfigured: configuredIds.has(album.id),
+    }));
+
+    // Sort: configured first, then by name
+    enriched.sort((a, b) => {
+      if (a.isConfigured !== b.isConfigured) return a.isConfigured ? -1 : 1;
+      return a.albumName.localeCompare(b.albumName);
+    });
+
+    return NextResponse.json({ albums: enriched });
+  } catch (err) {
+    console.error('[Admin] Failed to fetch albums from Immich:', err);
+    return NextResponse.json({ error: 'Failed to connect to Immich' }, { status: 502 });
+  }
+}