feat: SSH card UX, agent version sync, persistent ssh_admin_ok (0.11.5)

Silent SSH probe on host card open; manual test feedback auto-hides. Persist ssh_admin_ok in DB (migration 019). After agent update read version from host and refresh UI.

backend/app/schemas/list_models.py

@@ -30,6 +30,8 @@ class HostDetail(HostSummary):
     inventory: dict | None = None
     inventory_updated_at: datetime | None = None
     created_at: datetime | None = None
+    ssh_admin_ok: bool | None = None
+    ssh_admin_checked_at: datetime | None = None
 
 
 class HostListResponse(BaseModel):