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/agents/filesystem_agent.py

@@ -9,7 +9,7 @@ from typing import Any
 
 from langchain_core.tools import tool
 
-from app.ws_context import execute_on_client
+from shared.ws_context import execute_on_client
 
 
 @tool