Add Calendar dialog, Prescriptions & Messages pages, note delete confirm

- Appointments: a Calendar button next to Add opens a month-grid dialog
  (reuses the Calendar primitive + shared ScheduleList); the schedule day is
  marked and selecting it lists that day's appointments.
- Patients sub-nav: new Prescriptions page (mock list + KPIs) with a compact
  "New prescription" dialog reusing the patient quick-search pattern.
- Notes: deleting a note now goes through a reusable ConfirmDialog instead of
  deleting immediately.
- New top-level Messages page: two-pane email-style inbox (list + reading pane
  with mock reply composer), mirroring the Notes layout.
- Sidebar logo bumped from size-9 to size-10.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/lib/i18n/locales/en/translation.json

@@ -48,8 +48,10 @@
     "newChat": "New chat",
     "patients": "Patients",
     "appointments": "Appointments",
+    "prescriptions": "Prescriptions",
     "analysis": "Analysis",
     "notes": "Notes",
+    "messages": "Messages",
     "settings": "Settings",
     "notifications": "Notifications",
     "viewAllNotifications": "View all notifications",