v0.8.0 — Update-available detection (version chip + changelog)

Footer becomes a changelog chip and shows an 'Update available' badge when a
newer APP_VERSION exists upstream. Detection reads src/lib/version.ts from the
Gitea default branch (dms model) and compares — self-contained, no OTM control
plane. Adds src/lib/update-check.ts and GET /api/version (also a running-version
probe for the upcoming one-click rebuild).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/changelog.ts

@@ -8,6 +8,13 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.8.0",
+    date: "2026-06-15",
+    changes: [
+      "The app now tells you when a newer version is available — a little \"Update available\" badge appears in the bottom bar, and the version number opens the full changelog. (One-click updating is coming next.)",
+    ],
+  },
   {
     version: "0.7.0",
     date: "2026-06-15",