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/EventDetailSheet.swift

@@ -62,7 +62,7 @@ struct EventDetailSheet: View {
                             .fill(Color(hex: event.effectiveColor))
                             .frame(width: 6, height: 44)
                         VStack(alignment: .leading, spacing: 4) {
-                            Text(event.title)
+                            Text(event.renderTitle)
                                 .font(.title3.bold())
                             Text(event.calendarName)
                                 .font(.caption)
@@ -156,7 +156,7 @@ struct EventDetailSheet: View {
                 }
                 Button(L10n.t("common.cancel", appLang), role: .cancel) {}
             } message: {
-                Text("\"\(event.title)\" \(L10n.t("detail.delete_msg_suffix", appLang))")
+                Text("\"\(event.renderTitle)\" \(L10n.t("detail.delete_msg_suffix", appLang))")
             }
             .sheet(isPresented: $showCopySheet) {
                 EventEditorSheet(