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/env.ts

@@ -19,6 +19,10 @@ export interface Env {
   ADMIN_PASSWORD?: string;
   SITE_PASSWORD?: string;
   INSTALL_CONTENT_DIR?: string;
+  /** Whether the admin dashboard may ask GitHub for the latest release. */
+  UPDATE_CHECK: boolean;
+  /** Absolute site URL for sitemap, feed and JSON-LD. Overrides settings.yaml. */
+  SITE_URL?: string;
 }
 
 function parseEnv(): Env {
@@ -111,6 +115,11 @@ function parseEnv(): Env {
     ADMIN_PASSWORD: process.env.ADMIN_PASSWORD || undefined,
     SITE_PASSWORD: process.env.SITE_PASSWORD || undefined,
     INSTALL_CONTENT_DIR: process.env.INSTALL_CONTENT_DIR || undefined,
+    // On unless switched off: an instance that never learns about a security
+    // release is the worse default. Only `false` disables it, so a typo does
+    // not silently turn the check off.
+    UPDATE_CHECK: process.env.UPDATE_CHECK !== 'false',
+    SITE_URL: process.env.SITE_URL || undefined,
   };
 }