refactor: deduplicate shared code into shared/ module

Move duplicated files from chat + batch-agent into shared/:
- shared/ws_context.py — Redis-based tool call round-trip
- shared/llm.py — LiteLLM factory (get_llm, embed)
- shared/agents/ — 4 domain agents (task, note, project, timeline)

Update all service imports to use shared.* instead of app.*.
Delete 12 duplicated files across both services.

services/chat/app/routes.py

@@ -8,7 +8,7 @@ from fastapi.responses import JSONResponse
 from shared.schemas import ChatRequest
 
 from app.deep_agent import run_home
-from app.ws_context import clear_current_user, set_current_user
+from shared.ws_context import clear_current_user, set_current_user
 
 router = APIRouter(prefix="/chat", tags=["chat"])