feat(settings): settings UX polish + Calendars manager redesign

Settings:
- Event-form field rows show each field's own icon (shared
  EventFormFieldVisuals, reused by the editor and settings)
- Move "Add Quick Settings tile" to a top-level Settings hub row
- Notifications: reliable-delivery + snooze moved above the
  per-calendar block, which now folds behind one expandable section

Calendars manager:
- Local and synced calendars now use one collapsible group card
- Source-branded headers: each account shows its app's launcher icon
  (Google Calendar, DAVx5, …) loaded from PackageManager; local shows
  a device chip
- Per-account toggle-all switch (CalendarsViewModel.setAccountDisabled)
- Management action ("Add calendar" / "Manage in app") is a nested row
  inside the expanded group; removed the dead "Add account" row
- A fully deactivated account dims its header, not just the switch
- Group headers use the normal row colour; their options sit one tone
  darker (GroupedRow gains an optional container colour)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main/res/values/strings.xml

@@ -309,6 +309,7 @@
     <string name="reminder_custom_amount">Amount</string>
     <string name="reminder_custom_with_value">Custom (%1$s)</string>
     <string name="reminder_custom_set">Set</string>
+    <string name="settings_calendar_reminders_title">Per-calendar reminders</string>
     <string name="settings_calendar_reminders_hint">Override the default per calendar — separately for timed and all-day events. A calendar can keep the default, drop it, or set its own.</string>
     <string name="settings_calendar_reminder_inherits">Default (%1$s)</string>
     <string name="settings_reliable_delivery">Reliable delivery</string>
@@ -343,9 +344,11 @@
     <string name="calendars_add">Add calendar</string>
     <string name="calendars_disable_hint">Turn a calendar off to remove it from the app — its events, filters and pickers. Nothing is deleted, and you can turn it back on here anytime.</string>
     <string name="calendars_show_in_app_a11y">Show \"%1$s\" in the app</string>
+    <string name="calendars_account_toggle_all_a11y">Show all calendars from %1$s in the app</string>
     <string name="calendars_synced_header">Synced calendars</string>
     <string name="calendars_synced_hint">These come from accounts on your device. Create and edit them in their own app.</string>
     <string name="calendars_manage_in_app">Manage</string>
+    <string name="calendars_manage_account_a11y">Manage %1$s in its app</string>
     <string name="calendars_add_account">Add account</string>
     <string name="calendars_new_title">New calendar</string>
     <string name="calendars_edit_title">Edit calendar</string>