Implement FastAPI-based ASGI application served by uvicorn for
the CleverAgents server mode. Add health check endpoint, A2A
JSON-RPC routing, configurable host:port binding, and graceful
shutdown handling. Server launches via `agents server start`.
- Add FastAPI ASGI app factory at infrastructure/server/asgi_app.py
with /.well-known/agent.json (Agent Card), /health (liveness),
and /a2a (A2A JSON-RPC 2.0 dispatch via A2aLocalFacade)
- Add ServerLifecycle class at infrastructure/server/server_lifecycle.py
wrapping uvicorn.Server with SIGTERM/SIGINT graceful shutdown
- Add `agents server start` CLI command with --host, --port, --log-level
options, resolving defaults from Settings
- Add fastapi>=0.115.0 dependency to pyproject.toml (uvicorn already present)
- Add Behave BDD tests (features/server_lifecycle.feature, 20 scenarios)
- Add Robot Framework integration tests (robot/server_lifecycle.robot)
- Update CHANGELOG.md and vulture_whitelist.py
ISSUES CLOSED: #862
