feat(agent): Gradio-powered LangGraph agent chat with streaming, tool calls, file upload, conversation persistence

- Gradio 5.50.0 ChatInterface with type='messages' streaming
- LangGraph create_react_agent with InMemorySaver checkpointer
- 4 @tool functions: search_dashboards, get_health_summary, list_environments, get_task_status
- Structured ChatMessage metadata (7 discriminator types: stream_token, tool_start/end/error, confirm_required, confirm_resolved, error)
- HITL resume via second submit() with interrupt_before/Command
- Dual-identity RBAC: service JWT + user JWT for tool calls
- File upload (10 MB limit, pdfplumber/xlsx/JSON parser)
- Conversation persistence via POST /api/agent/conversations/save
- REST API: list, history, archive conversations; multi-tab gate; LLM config
- LLM provider selection via Admin -> LLM Settings (assistant_planner_provider)
- Svelte 5 AgentChatModel with stream event queue, dedup, stream_status watcher
- MarkdownRenderer using svelte-markdown with semantic Tailwind tokens
- ToolCallCard (3 states: executing/completed/failed)
- ConversationList with search, date grouping, infinite scroll
- ConnectionIndicator with Gradio health status
- /agent route with two-column layout
- Vite proxy /api/agent/gradio -> Gradio SSE
- Fixed: not_() SQLAlchemy operator, route collision with _admin_routes
- Fixed: conversation_id -> id normalization, .pyc cache staleness
- Fixed: event.data array parsing (Gradio returns [jsonStr, null])
- Requirements pinned: gradio==5.50.0, pydantic>=2.7,<=2.12.3

backend/requirements.txt

@@ -24,9 +24,9 @@ jsonschema-specifications==2025.9.1
 keyring==25.7.0
 more-itertools==10.8.0
 pycparser==2.23
-pydantic==2.12.5
+pydantic>=2.7,<=2.12.3
 pydantic-settings
-pydantic_core==2.41.5
+pydantic_core==2.41.4
 python-multipart==0.0.21
 PyYAML==6.0.3
 passlib[bcrypt]
@@ -62,3 +62,9 @@ sqlparse>=0.5.0
 testcontainers[postgres]>=4.0
 aiofiles>=24.1.0
 aiosmtplib>=3.0.2
+gradio==5.50.0
+langgraph>=0.2
+langchain-core>=0.3
+langchain-openai>=0.3
+langgraph-checkpoint-postgres
+pdfplumber