fix(dashboard): persist widget drag-drop order (validator was dropping it)

N46 (a147cbc) shipped the drag-drop UI + optimistic mutation, but the
PATCH body was being silently stripped by the user-preferences Zod
validator — `dashboardWidgetOrder` wasn't in the schema, so Zod's
default strip-unknown-keys behaviour dropped it before the DB write.

Symptom: drop the widget in a new position → UI reflects the order
optimistically → onSettled invalidates + refetches → GET returns the
unchanged-on-disk order → dashboard snaps back to the original
layout.

Added the field to updateUserPreferencesSchema with the same loose
shape (array-of-string) the schema declared 100+ lines earlier.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/validators/user-preferences.ts

@@ -21,6 +21,12 @@ export const updateUserPreferencesSchema = z.object({
    * update.
    */
   dashboardWidgets: z.record(z.string(), z.boolean()).optional(),
+  /**
+   * Rep-chosen dashboard widget order (drag-drop). Missing ids fall
+   * through to registry order so newly-added widgets always surface.
+   * Kept loose (array-of-string) for the same reason as above.
+   */
+  dashboardWidgetOrder: z.array(z.string()).optional(),
 });
 
 export type UpdateUserPreferencesInput = z.infer<typeof updateUserPreferencesSchema>;