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>

lib/__tests__/urls.test.ts

@@ -17,6 +17,7 @@ import {
   assetPlaceholder,
   assetExifSummary,
   assetAspectRatio,
+  assetCaption,
 } from '@/lib/urls';
 
 describe('imageUrl', () => {
@@ -168,3 +169,58 @@ describe('assetAspectRatio', () => {
     ).toBeUndefined();
   });
 });
+
+describe('assetCaption', () => {
+  /** An asset carrying nothing but the description under test. */
+  const withDescription = (description: string | null) => ({
+    exifInfo: {
+      make: null,
+      model: null,
+      lensModel: null,
+      focalLength: null,
+      fNumber: null,
+      exposureTime: null,
+      iso: null,
+      exifImageWidth: null,
+      exifImageHeight: null,
+      latitude: null,
+      longitude: null,
+      city: null,
+      state: null,
+      country: null,
+      dateTimeOriginal: null,
+      description,
+    },
+  });
+
+  it('returns the description when captions are shown', () => {
+    expect(assetCaption(withDescription('A gull over the harbour'), true)).toBe(
+      'A gull over the harbour',
+    );
+  });
+
+  it('trims surrounding whitespace', () => {
+    expect(assetCaption(withDescription('  Low tide\n'), true)).toBe('Low tide');
+  });
+
+  it.each([
+    ['null', null],
+    ['empty', ''],
+    ['whitespace only', '   \n\t '],
+  ])('returns undefined for a %s description, leaving alt=""', (_label, value) => {
+    expect(assetCaption(withDescription(value), true)).toBeUndefined();
+  });
+
+  it('returns undefined when the asset has no exifInfo at all', () => {
+    expect(assetCaption({ exifInfo: undefined }, true)).toBeUndefined();
+  });
+
+  /**
+   * The point of #506: the description is the one field that can hold private
+   * notes. Alt text publishes it as surely as a visible caption does, so the
+   * caption switch has to gate it too.
+   */
+  it('withholds the description when captions are switched off', () => {
+    expect(assetCaption(withDescription('Client hates this crop'), false)).toBeUndefined();
+  });
+});