fix(prod): harden production configuration for launch

- Gate Swagger/ReDoc/OpenAPI behind DEBUG (no public API schema in prod)
- Sentry send_default_pii only in dev (no auth headers/bodies in events)
- Remove alembic from Dockerfile CMD (releaseCommand owns migrations; CMD copy raced across replicas/restarts)
- Decouple rate limiting from DEBUG via RATE_LIMIT_ENABLED (PR envs with DEBUG=true were unlimited); tests disable the live limiter in conftest
- max_instances=1 on the 4 scheduler jobs missing it
- Boot-time failure when SELF_SERVE_ENABLED without RESEND_API_KEY/ANTHROPIC_API_KEY/FRONTEND_URL
- Reject localhost OAUTH_REDIRECT_BASE outside DEBUG
- pool_pre_ping + pool_recycle on the app engine
- Frontend: DEV-gate stale-async console.warn; document VITE_SELF_SERVE_ENABLED fallback semantics in Dockerfile

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/pages/AssistantChatPage.tsx

@@ -266,11 +266,13 @@ export default function AssistantChatPage() {
   const loadedChatIdsRef = useRef<Set<string>>(new Set())
   const guardCurrentChat = useCallback((expectedChatId: string, source: string) => {
     if (currentChatRef.current === expectedChatId) return true
-    console.warn('[AssistantChat] Discarded stale async result', {
-      source,
-      expectedChatId,
-      currentChatId: currentChatRef.current,
-    })
+    if (import.meta.env.DEV) {
+      console.warn('[AssistantChat] Discarded stale async result', {
+        source,
+        expectedChatId,
+        currentChatId: currentChatRef.current,
+      })
+    }
     return false
   }, [])