Dashboard customize mode: reorder/hide modules and individual rows, layout saved server-side (GET/PUT /api/prefs/dashboard)

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/store/store.go

@@ -17,7 +17,8 @@ type Terminal struct {
 
 type State struct {
 	Terminals []Terminal           `json:"terminals"`
-	Sessions  map[string]time.Time `json:"sessions"` // token -> expiry
+	Sessions  map[string]time.Time `json:"sessions"`            // token -> expiry
+	Dashboard json.RawMessage      `json:"dashboard,omitempty"` // UI layout prefs, opaque to the server
 }
 
 type Store struct {