Add birthday feature (iOS)

- LocalCalendar/CalEvent gain is_birthday + birthday fields; API sends
  rrule/external_uid/birth_year and can create/update birthday calendars
- BirthdaysImporter: mirrors Contacts birthdays into a chosen birthday
  calendar, reconciling by external_uid (leaves manual entries untouched)
- AccountsView: "birthday calendar" toggle + notify-days when creating a
  calendar, and a "Birthdays from Contacts" section (enable + target + sync now)
- FAB long-press menu -> "New birthday" opens a minimal name+date mask
  (BirthdayEditorSheet) targeting birthday calendars, with year-unknown option
- Event bars render display_title (age) and a cake icon via EventLabel
- NSContactsUsageDescription added to both app build configs

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

Calendarr iOS/Views/Calendar/DayView.swift

@@ -81,7 +81,7 @@ struct DayView: View {
             HStack(spacing: 6) {
                 ForEach(allDayEvents) { ev in
                     Button(action: { onEventTap(ev) }) {
-                        Text(ev.title)
+                        EventLabel(event: ev)
                             .font(.caption.weight(.medium))
                             .foregroundStyle(.white)
                             .padding(.horizontal, 8).padding(.vertical, 4)