fix(chat): resolve Auto-route failover event-loop freeze (#812)

Root cause: ensure_structured_column() executed a synchronous blocking
engine.connect().execute(SELECT information_schema.columns ...) inside the
async request path (_build_chat_history / _maybe_compress_history), freezing
the uvicorn event loop and hanging all endpoints (~200s, recovered only by
docker restart).

Fix:
- chat_context.py: remove per-request ensure_structured_column() calls; run
  once idempotently at app startup (main.py lifespan). Use CURRENT_DATABASE()
  for PostgreSQL compatibility.
- main.py: add startup-only ensure_structured_column() hook (try/except).
- llm_client.py: trust_env=False + bounded httpx.Timeout/wait_for so broken
  endpoints fail fast instead of hanging the event loop.
- chat_service.py: run media generation in a background daemon thread with its
  own event loop (_launch_media_task_bg) so SSE end does not cancel image/video
  tasks (#811); remove TEMP faulthandler diagnostic.

Safe-align: persist accumulated live container changes (admin/*, knowledge,
market, models, config, observability, mcp_client, platform_knowledge,
im_bot_platform, chat_media, capability_registry, requirements) and add
workflow_templates.

Verified: live failover test (model-006 -> conn-refused) returns in ~1.9s with
concurrent login 0.83s/200; event-loop responsiveness restored (sub-second).

backend/python/app/api/admin/analytics_admin.py

@@ -316,7 +316,7 @@ async def create_dashboard(
         config_json = json.loads('[{"type":"stat","title":"暂无数据","metric":"none","chart_type":"number"}]')
 
     if is_default:
-        db.execute(text("UPDATE analytics_dashboards SET is_default=0"))
+        db.execute(text("UPDATE analytics_dashboards SET is_default=false"))
 
     db.execute(text("""
         INSERT INTO analytics_dashboards (id, name, description, config, is_default, created_by)
@@ -332,7 +332,7 @@ async def create_dashboard(
 @router.delete("/dashboards/{dashboard_id}")
 async def delete_dashboard(dashboard_id: str, db: Session = Depends(get_db), user=Depends(get_current_user)):
     """删除仪表盘"""
-    db.execute(text("DELETE FROM analytics_dashboards WHERE id=:id AND is_default=0"), {"id": dashboard_id})
+    db.execute(text("DELETE FROM analytics_dashboards WHERE id=:id AND is_default=false"), {"id": dashboard_id})
     db.commit()
     return {"code": 200, "data": {"message": "仪表盘已删除"}}