feat: Windows admin in Settings UI and WinRM host test (0.10.1)

Store domain admin in ui_settings (DB overrides env); qwinsta/logoff use effective config.
Host card: POST /hosts/{id}/actions/winrm-test via pywinrm.

backend/app/models/ui_settings.py

@@ -1,4 +1,4 @@
-from sqlalchemy import Boolean
+from sqlalchemy import Boolean, String, Text
 from sqlalchemy.orm import Mapped, mapped_column
 
 from app.database import Base
@@ -13,3 +13,5 @@ class UiSettings(Base):
 
     id: Mapped[int] = mapped_column(primary_key=True)
     show_sidebar_system_stats: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    win_admin_user: Mapped[str | None] = mapped_column(String(256), nullable=True)
+    win_admin_password: Mapped[str | None] = mapped_column(Text, nullable=True)