fix(cloudflare): fix delete_tunnel subdomain format and add startup config check

- Fix delete_tunnel calls to use correct subdomain format (instance-{id[:8]})
- Add Cloudflare configuration check at startup with clear warnings
- Help diagnose why tunnels aren't being created

apps/api/src/main.py

@@ -229,6 +229,18 @@ async def on_startup():
 
     # Seed built-in data
     await seed_builtin_tool_types()
+
+    # Check Cloudflare configuration
+    settings = Settings()
+    if settings.cloudflare_api_token and settings.cloudflare_account_id and settings.cloudflare_zone_id and settings.cloudflare_base_domain:
+        logger.info("Cloudflare tunnel configuration detected: base_domain=%s", settings.cloudflare_base_domain)
+    else:
+        logger.warning(
+            "Cloudflare tunnel configuration incomplete. "
+            "Tunnels will not be created. Set CLOUDFLARE_API_TOKEN, "
+            "CLOUDFLARE_ACCOUNT_ID, CLOUDFLARE_ZONE_ID, and CLOUDFLARE_BASE_DOMAIN."
+        )
+
     logger.info("Startup complete.")
 
 app.include_router(health_router)