feat(reminders): snooze + dismiss notification actions

Add "Snooze" and "Dismiss" action buttons to reminder notifications.

The app is otherwise pure provider-broadcast (the Etar model): the calendar
provider fires EVENT_REMINDER and we post the notification, then mark the
CalendarAlerts row fired. A snoozed reminder has no provider backing — its
row is already fired — so snooze self-schedules an exact alarm to re-show
the same notification, while primary delivery is left unchanged.

- ReminderActionReceiver (not exported): SNOOZE cancels + schedules a
  re-show, DISMISS cancels, SHOW (the alarm) re-posts so it can be snoozed
  or dismissed again.
- ReminderSnoozeScheduler: setExactAndAllowWhileIdle, with an inexact
  allow-while-idle fallback if exact alarms are revoked (API 31-32).
- ReminderNotifier: two actions + cancel().
- snoozeMinutes pref (default 10) in Settings -> Notifications, OptionPicker
  presets 5/10/15/30/60.
- Manifest: USE_EXACT_ALARM + SCHEDULE_EXACT_ALARM (maxSdk 32) + receiver.
- New ic_notification_snooze/_dismiss drawables, duration plurals, en+de
  strings, snooze-pref tests.

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

app/src/main/res/drawable/ic_notification_dismiss.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Monochrome notification-action mark: Material "close" glyph. -->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24"
+    android:tint="?attr/colorControlNormal">
+    <path
+        android:fillColor="@android:color/white"
+        android:pathData="M19,6.41L17.59,5 12,10.59 6.41,5 5,6.41 10.59,12 5,17.59 6.41,19 12,13.41 17.59,19 19,17.59 13.41,12z" />
+</vector>