feat(reminders): configurable all-day reminder fire time

All-day events live at UTC midnight, so a raw "1 day before" reminder
fires at an off hour (02:00 local in CEST) rather than the morning. Add a
global "all-day reminder time" setting (default 09:00) and encode it into
the provider MINUTES offset so the reminder lands at the chosen wall-clock
time the day before instead.

- AllDayReminderEncoding: pure to/from provider-minutes helpers, keeping
  the form/UI/diff in whole-day "semantic" minutes and converting only at
  the Reminders read/write boundary (insertEvent, reconcileReminders,
  EventDetailMapper). Covers DST, negative offsets, and pre-existing rows.
- SettingsPrefs.allDayReminderTimeMinutes (default 540) threaded from the
  repository into the data-source write paths.
- Settings: a time-picker row, plus a shared TimePickerAlert lifted from
  the event editor.
- Fix the time picker's 12/24-hour detection: honour an explicit system
  override, else fall back to the device locale rather than the app's
  per-app language, so it matches the rest of the device.

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

app/src/main/AndroidManifest.xml

@@ -5,6 +5,13 @@
     <uses-permission android:name="android.permission.READ_CALENDAR" />
     <uses-permission android:name="android.permission.WRITE_CALENDAR" />
     <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
+    <!--
+      Lets the "Reliable delivery" setting open the direct system dialog to
+      exempt Calendula from battery optimisation (so reminder broadcasts aren't
+      delayed by Doze). Used only to launch that dialog; falls back to the
+      battery-optimisation list if the OS declines the direct intent.
+    -->
+    <uses-permission android:name="android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS" />
 
     <!-- Package visibility (Android 11+): without this, getLaunchIntentForPackage
          returns null and the calendar manager's per-account "manage" button can't