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/redis_consumer.py

@@ -17,7 +17,7 @@ from shared.redis import redis_client, ws_out_channel
 from app.deep_agent import run_floating_stream, run_home_stream
 from app.memory_middleware import MemoryMiddleware
 from app.output_formatter import StreamFormatter
-from app.ws_context import clear_current_user, set_current_user
+from shared.ws_context import clear_current_user, set_current_user
 from app import tracing
 
 logger = logging.getLogger(__name__)