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/services/win_admin_settings.py

@@ -0,0 +1,82 @@
+"""Effective Windows domain admin credentials (DB overrides env)."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from sqlalchemy.orm import Session
+
+from app.config import get_settings
+from app.models.ui_settings import UI_SETTINGS_ROW_ID, UiSettings
+
+
+@dataclass(frozen=True)
+class WinAdminConfig:
+    user: str
+    password: str
+    source: str  # env | db
+
+    @property
+    def configured(self) -> bool:
+        return bool(self.user.strip() and self.password.strip())
+
+
+def _win_admin_from_env() -> WinAdminConfig:
+    settings = get_settings()
+    return WinAdminConfig(
+        user=settings.sac_win_admin_user.strip(),
+        password=settings.sac_win_admin_password,
+        source="env",
+    )
+
+
+def get_effective_win_admin_config(db: Session | None = None) -> WinAdminConfig:
+    if db is None:
+        from app.database import SessionLocal
+
+        session = SessionLocal()
+        try:
+            return get_effective_win_admin_config(session)
+        finally:
+            session.close()
+
+    row = db.get(UiSettings, UI_SETTINGS_ROW_ID)
+    env_cfg = _win_admin_from_env()
+    if row is None:
+        return env_cfg
+
+    user = (row.win_admin_user or "").strip() or env_cfg.user
+    password = (row.win_admin_password or "") or env_cfg.password
+    has_db_values = bool((row.win_admin_user or "").strip() or (row.win_admin_password or "").strip())
+    return WinAdminConfig(
+        user=user,
+        password=password,
+        source="db" if has_db_values else env_cfg.source,
+    )
+
+
+def upsert_win_admin_settings(
+    db: Session,
+    *,
+    user: str | None = None,
+    password: str | None = None,
+) -> WinAdminConfig:
+    row = db.get(UiSettings, UI_SETTINGS_ROW_ID)
+    env_cfg = _win_admin_from_env()
+    if row is None:
+        row = UiSettings(
+            id=UI_SETTINGS_ROW_ID,
+            show_sidebar_system_stats=True,
+            win_admin_user=env_cfg.user or None,
+            win_admin_password=env_cfg.password or None,
+        )
+        db.add(row)
+
+    if user is not None and user.strip():
+        row.win_admin_user = user.strip()
+    if password is not None and password.strip():
+        row.win_admin_password = password
+
+    db.commit()
+    db.refresh(row)
+    return get_effective_win_admin_config(db)