fix(agent): auto-start scenario chat, robust HITL resume, strict service auth

- frontend: fix auto-start on dashboards->/agent navigation (undefined params
  ReferenceError), route initial connect through ConnectionManager with auto-retry,
  reset runModel on objectId change and failed recovery
- agent: fix closure-over-loop-variable bug in _inject_env_id_into_tools (env now
  resolved from request-local ContextVar; idempotent wrapping), make
  execute_dashboard_result.result_key optional, resilient checkpoint resume with
  ToolMessage repair + direct-tool fallback, remove dead fast-path, consolidate
  tool_call parsing in _tool_resolver, context-safe ContextVar resets
- backend: llm-config gated by strict service-only auth (no user-JWT fallback),
  tighten idempotent run reuse (dashboard/env/intent match + 6h staleness),
  terminal event transitions run.status to COMPLETED/FAILED/CANCELLED,
  null-safe metric parsing in dashboard query model
- run.sh/docker-compose: require SERVICE_JWT (random per-run secret) instead of
  public default

backend/src/app.py

@@ -435,9 +435,12 @@ async def global_exception_handler(request: Request, exc: Exception):
 async def network_error_handler(request: Request, exc: NetworkError):
     with belief_scope("network_error_handler"):
         logger.explore("Network error", error=str(exc))
-        return HTTPException(
+        return JSONResponse(
             status_code=503,
-            detail="Environment unavailable. Please check if the Superset instance is running.",
+            content={
+                "detail": "Environment unavailable. Please check if the Superset instance is running.",
+                "path": request.url.path,
+            },
         )