feat: add customer notes UI to portal and staff views (GRO-178)

- Add customerNotes field to Appointment type
- Add read-only customer notes display in staff appointment detail modal
- Add customer notes textarea with save, char counter (500 max), and disabled state
- Wire up PATCH /api/portal/appointments/:id/notes in portal UI
- Update mockData with customerNotes field

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/types/src/index.ts

@@ -110,6 +110,7 @@ export interface Appointment {
   confirmedAt: string | null;
   cancelledAt: string | null;
   confirmationToken: string | null;
+  customerNotes: string | null;
   createdAt: string;
   updatedAt: string;
 }