feat(api): Android self-update endpoints proxied from Gitea releases (M5)

GET /api/v1/app/android/latest reads the latest Gitea release with the
server token (cached for 10 minutes); the download endpoint caches the
APK under /updates, verifies its SHA-256 and serves it with Range.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/i18n/locales/en/errors.json

@@ -71,5 +71,8 @@
   },
   "wave": {
     "session_not_found": "The wave session has ended"
+  },
+  "app": {
+    "update_unavailable": "Update is unavailable"
   }
 }

packages/i18n/locales/ru/errors.json

@@ -71,5 +71,8 @@
   },
   "wave": {
     "session_not_found": "Сессия волны завершена"
+  },
+  "app": {
+    "update_unavailable": "Обновление недоступно"
   }
 }