feat: RDG session flap rule, qwinsta/logoff queue and dashboard UI (0.9.13)

Detect 302→303 within 1–10s, Problem with 30s dedup, rdg_flap flag.
Agent command poll API, admin qwinsta/logoff from Overview. Migration 016.

backend/app/models/__init__.py

@@ -1,3 +1,4 @@
+from app.models.agent_command import AgentCommand
 from app.models.api_key import ApiKey
 from app.models.event import Event
 from app.models.host import Host
@@ -16,6 +17,7 @@ from app.models.mobile_refresh_token import MobileRefreshToken
 
 __all__ = [
     "ApiKey",
+    "AgentCommand",
     "Event",
     "Host",
     "NotificationChannel",