release: v0.13.0 (#535)

Twenty-nine commits since v0.12.0. See CHANGELOG.md for the full list
and the upgrade notes.

Ten additions — the SEO package (site URL, robots.txt, sitemap.xml,
JSON-LD), slideshow mode, opt-in original downloads, copy-link,
previous/next album navigation, alt text from the Immich description,
per-album location precision, the update notice, a Help tab, and a
subpage cover grid separate from its photo grid. Two fixes: CJK album
slugs, and the lightbox control bar.

Photo of the Day (#476) was built on `dev` and reverted as not planned;
it never appears in a release.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01DmsHVRL9yQvckUB1ZpVWre

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: ralksta <ralksta@users.noreply.github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

app/admin/components/SettingsEditor.tsx

@@ -8,12 +8,20 @@ import SaveBar from './SaveBar';
 // Direct import from the theme module, not from '@/lib/config': the config
 // index pulls in `fs` and cannot be bundled into a client component.
 import { DEFAULT_PRESET } from '@/lib/config/theme';
-import { resolveExifDisplay, resolveWatermarkOpacity } from '@/lib/config/schema';
+import {
+  PHOTO_GRID_COLUMNS_MAX,
+  PHOTO_GRID_COLUMNS_MIN,
+  PHOTO_GRID_GAP_MAX,
+  resolveExifDisplay,
+  resolveWatermarkOpacity,
+} from '@/lib/config/schema';
 import { SUPPORTED_LOCALES } from '@/lib/i18n';
 
 interface Settings {
   title?: string;
   subtitle?: string;
+  /** Absolute site URL for sitemap, feed and structured data (#472). */
+  url?: string;
   lang?: string;
   sitePassword?: string;
   mode?: 'light' | 'dark' | 'auto';
@@ -306,6 +314,11 @@ export default function SettingsEditor({ section }: SettingsEditorProps) {
     ? (section as string)
     : 'general';
   const [settings, setSettings] = useState<Settings>({});
+  /** Resolved site URL and its origin, so the panel can name SITE_URL (#472). */
+  const [siteUrlInfo, setSiteUrlInfo] = useState<{
+    effective: string | null;
+    source: 'env' | 'settings' | 'none';
+  } | null>(null);
   const [loading, setLoading] = useState(true);
   // Collapsed by default: the four metadata switches are a detail of one
   // decision, and showing them permanently is what made the section a wall (#510).
@@ -418,8 +431,9 @@ export default function SettingsEditor({ section }: SettingsEditorProps) {
     try {
       const res = await fetch('/api/admin/settings');
       if (res.ok) {
-        const { settings: data } = await res.json();
+        const { settings: data, siteUrl } = await res.json();
         setSettings(data || {});
+        setSiteUrlInfo(siteUrl ?? null);
       }
     } catch (err) {
       console.error('Failed to load settings:', err);
@@ -1520,11 +1534,13 @@ export default function SettingsEditor({ section }: SettingsEditorProps) {
 
               <div className="admin-field-row">
                 <div className="admin-field">
-                  <label>Columns (1 - 6)</label>
+                  <label>
+                    Columns ({PHOTO_GRID_COLUMNS_MIN} - {PHOTO_GRID_COLUMNS_MAX})
+                  </label>
                   <input
                     type="number"
-                    min={1}
-                    max={6}
+                    min={PHOTO_GRID_COLUMNS_MIN}
+                    max={PHOTO_GRID_COLUMNS_MAX}
                     value={settings.grid?.columns ?? 3}
                     onChange={(e) => update('grid.columns', parseInt(e.target.value) || 3)}
                   />
@@ -1534,7 +1550,7 @@ export default function SettingsEditor({ section }: SettingsEditorProps) {
                   <input
                     type="number"
                     min={0}
-                    max={48}
+                    max={PHOTO_GRID_GAP_MAX}
                     value={settings.grid?.gap ?? 12}
                     onChange={(e) => update('grid.gap', parseInt(e.target.value) || 0)}
                   />
@@ -1786,6 +1802,28 @@ export default function SettingsEditor({ section }: SettingsEditorProps) {
                 </div>
               </div>
 
+              <div className="admin-field">
+                <label>Site URL</label>
+                <input
+                  value={settings.url || ''}
+                  onChange={(e) => update('url', e.target.value)}
+                  placeholder="https://folio.example"
+                />
+                <p style={{ fontSize: '0.8rem', opacity: 0.7, marginTop: '4px' }}>
+                  Needed for <code>sitemap.xml</code>, the feed and structured data — those are
+                  generated without a request, so the address cannot be derived from it. Leave empty
+                  and the sitemap stays empty rather than guessing.
+                  {siteUrlInfo?.source === 'env' && (
+                    <>
+                      <br />
+                      Currently supplied by the <code>SITE_URL</code> environment variable (
+                      <code>{siteUrlInfo.effective}</code>). A value entered here takes precedence
+                      once saved.
+                    </>
+                  )}
+                </p>
+              </div>
+
               <div className="admin-field">
                 <label>SEO Meta Title</label>
                 <input