M5: reminders onboarding, Settings screen & per-list overrides

Reminders onboarding & polish, plus the Settings screen (landed early).

- One-time reminder onboarding gate after the provider grant
  (ReminderOnboardingScreen + OnboardingScaffold), requesting
  POST_NOTIFICATIONS on API 33+; choice recorded in prefs.
- Settings screen, structured after Calendula as a category hub with
  sliding sub-screens (CollapsingScaffold + grouped rows + full-screen
  OptionPicker): About card, Appearance (theme, dynamic colour), Task
  form (default edit-form fields, default list, add-a-subtask-row
  opt-out), Reminders, Language, and Report a problem. Reached via an
  expressive shaped action button (MaterialShapes.Cookie4Sided) on the
  lists overview. Back from a sub-screen returns to the hub.
- Reminders: master enable toggle (gates the whole engine; re-requests
  the notification permission), a default lead time with a Custom
  amount/unit editor, an Android-12 exact-alarm status row, and
  per-list overrides of the default (Inherit / None / custom lead),
  honoured by ReminderScheduler per task.
- Per-app language (AppLanguage + locales_config.xml + appcompat
  locales service); add-a-subtask-row opt-out wired into the task list.

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

app/src/main/AndroidManifest.xml

@@ -36,6 +36,7 @@
         android:fullBackupContent="@xml/backup_rules"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"
+        android:localeConfig="@xml/locales_config"
         android:roundIcon="@mipmap/ic_launcher_round"
         android:supportsRtl="true"
         android:theme="@style/Theme.Floret"
@@ -76,6 +77,17 @@
                 <data android:scheme="content" android:host="org.dmfs.tasks" />
             </intent-filter>
         </receiver>
+
+        <!-- Persists the per-app language on API < 33, where the platform
+             per-app-languages API is unavailable. On 33+ this is a no-op. -->
+        <service
+            android:name="androidx.appcompat.app.AppLocalesMetadataHolderService"
+            android:enabled="false"
+            android:exported="false">
+            <meta-data
+                android:name="autoStoreLocales"
+                android:value="true" />
+        </service>
     </application>
 
 </manifest>