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/batch-agent/app/main.py

@@ -14,6 +14,14 @@ from __future__ import annotations
 
 import asyncio
 import logging
+import sys
+from pathlib import Path
+
+# Ensure the repo root is on sys.path so ``shared`` is importable when
+# running locally (in Docker the COPY already places it at /app/shared/).
+_repo_root = str(Path(__file__).resolve().parents[3])
+if _repo_root not in sys.path:
+    sys.path.insert(0, _repo_root)
 
 from contextlib import asynccontextmanager
 from typing import AsyncGenerator