feat(store): GlobalOverrideStore + SetOverrideOnUntil

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/backend/internal/store/store.go

@@ -699,3 +699,66 @@ func (s *ScreenScheduleStore) ListEnabled(ctx context.Context) ([]*ScreenSchedul
 	}
 	return out, rows.Err()
 }
+
+// SetOverrideOnUntil setzt oder löscht den per-Screen-Override (null = löschen).
+func (s *ScreenScheduleStore) SetOverrideOnUntil(ctx context.Context, screenID string, until *time.Time) error {
+	_, err := s.pool.Exec(ctx,
+		`insert into screen_schedules (screen_id, override_on_until)
+		 values ($1, $2)
+		 on conflict (screen_id) do update
+		   set override_on_until = excluded.override_on_until`,
+		screenID, until)
+	return err
+}
+
+// ------------------------------------------------------------------
+// GlobalOverrideStore
+// ------------------------------------------------------------------
+
+// GlobalOverride beschreibt einen aktiven globalen Display-Override.
+type GlobalOverride struct {
+	Type  string    `json:"type"`   // "on" oder "off"
+	Until time.Time `json:"until"`
+	SetAt time.Time `json:"set_at"`
+}
+
+// GlobalOverrideStore verwaltet den globalen Display-Override (max. 1 Zeile).
+type GlobalOverrideStore struct{ pool *pgxpool.Pool }
+
+func NewGlobalOverrideStore(pool *pgxpool.Pool) *GlobalOverrideStore {
+	return &GlobalOverrideStore{pool: pool}
+}
+
+// Get lädt den aktuellen globalen Override. Gibt nil zurück wenn keiner gesetzt ist.
+func (s *GlobalOverrideStore) Get(ctx context.Context) (*GlobalOverride, error) {
+	var o GlobalOverride
+	err := s.pool.QueryRow(ctx,
+		`select type, until, set_at from global_override where id = 1`).
+		Scan(&o.Type, &o.Until, &o.SetAt)
+	if errors.Is(err, pgx.ErrNoRows) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &o, nil
+}
+
+// Upsert setzt oder überschreibt den globalen Override.
+func (s *GlobalOverrideStore) Upsert(ctx context.Context, overrideType string, until time.Time) error {
+	_, err := s.pool.Exec(ctx,
+		`insert into global_override (id, type, until, set_at)
+		 values (1, $1, $2, now())
+		 on conflict (id) do update
+		   set type   = excluded.type,
+		       until  = excluded.until,
+		       set_at = excluded.set_at`,
+		overrideType, until)
+	return err
+}
+
+// Delete entfernt den globalen Override.
+func (s *GlobalOverrideStore) Delete(ctx context.Context) error {
+	_, err := s.pool.Exec(ctx, `delete from global_override where id = 1`)
+	return err
+}