Part of #4084 - FastAPI Router Migration Proposal ## Scope Migrate the agents API from @webmethod decorators to standard FastAPI routers. ## Tasks - [ ] Extract Protocol to agents/service.py (remove @webmethod) - [ ] Create agents/models.py with Pydantic request/response models - [ ] Create agents/routes.py with FastAPI router - [ ] Register router in router registry - [ ] Update agent provider implementations - [ ] Update tests ## Dependencies - Requires Phase 1 infrastructure (#4084) Related to #4084