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/redis_consumer.py

@@ -18,7 +18,7 @@ from typing import Any
 from shared.redis import redis_client, batch_request_channel, ws_out_channel
 
 import app.tracing as tracing
-from app.ws_context import set_current_user, clear_current_user
+from shared.ws_context import set_current_user, clear_current_user
 
 logger = logging.getLogger(__name__)