fix(agent): seed trace_id for agent process lifecycle

Agent logs had trace_id='no-trace' because the Gradio process
never called seed_trace_id(). The CotJsonFormatter reads trace_id
from ContextVar — without seeding, it defaults to empty string
displayed as 'no-trace'.

Fix:
- app.py: seed_trace_id() on every agent_handler invocation
- run.py: seed_trace_id() on agent startup (for LLM config fetch)

Each Gradio submit gets a fresh trace_id, making agent logs
correlatable with downstream FastAPI calls.

backend/src/agent/run.py

@@ -12,6 +12,7 @@ import os
 import socket
 import httpx
 
+from src.core.cot_logger import seed_trace_id
 from src.core.logger import logger
 
 FASTAPI_URL = os.getenv("FASTAPI_URL", "http://localhost:8000")
@@ -85,6 +86,8 @@ if __name__ == "__main__":
     from src.agent.context import set_service_jwt
     from src.agent.langgraph_setup import configure_from_api, init_checkpointer
 
+    seed_trace_id()  # Seed trace for agent startup lifecycle
+
     # Propagate SERVICE_JWT to ContextVar for tool calls
     service_token = os.getenv("SERVICE_JWT", "")
     if service_token: