Implement cross-domain support for OAuth and API requests

- Updated frontend to use `https://cms.gallus-pub.ch` as the API base URL.
- Configured cookies with `SameSite=None` and `Secure` for production in `auth.ts`.
- Enhanced `fly.toml` to include `FRONTEND_URL`, `CORS_ORIGIN`, and `GITEA_REDIRECT_URI`.
- Adjusted `.gitignore` to ignore `/ai/` directory.

backend/fly.toml

@@ -10,6 +10,10 @@ primary_region = "ams"
   GITEA_URL = "https://git.bookageek.ch"
   DATABASE_PATH = "/app/data/gallus_cms.db"
   GIT_WORKSPACE_DIR = "/app/data/workspace"
+  # Cross-site frontend and OAuth
+  FRONTEND_URL = "https://gallus-pub.ch"
+  CORS_ORIGIN = "https://gallus-pub.ch"
+  GITEA_REDIRECT_URI = "https://cms.gallus-pub.ch/api/auth/callback"
 
 [http_service]
   internal_port = 8080