fix(agent): minimal safety net, zero-config router, LLM provider status UI

- Remove deterministic intent matching (keyword lists, infer_tool,
  fast_confirmation, negation guard, classification sets)
- Embedding descriptions auto-generated from tool docstrings
- LLM provider health endpoint GET /api/agent/llm-status
- 3 error codes: LLM_PROVIDER_UNAVAILABLE, LLM_TIMEOUT, LLM_AUTH_ERROR
- Frontend banner with auto-retry 30s + input disable
- i18n for LLM status messages (assistant.json ru/en)
- 138 passing backend tests

backend/src/app.py

@@ -33,6 +33,7 @@ from .api.routes import (
     admin,
     admin_api_keys,
     agent_conversations,
+    agent_status,
     agent_superset,
     agent_superset_explore,
     assistant,
@@ -411,6 +412,7 @@ app.include_router(reports.router)
 app.include_router(assistant.router, prefix="/api/assistant", tags=["Assistant"])
 app.include_router(agent_conversations.agent_router, tags=["Agent"])
 app.include_router(agent_conversations.router, tags=["Assistant"])
+app.include_router(agent_status.router)
 app.include_router(agent_superset.router, tags=["Agent Superset"])
 app.include_router(agent_superset_explore.router, tags=["Agent Superset"])
 app.include_router(clean_release.router)