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/res/xml/locales_config.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+    The languages Floret ships translations for. Single source of truth: each
+    entry needs a matching res/values-<tag>/strings.xml, and is surfaced in both
+    the in-app language picker (parsed at runtime by AppLanguage) and the system
+    per-app language settings (Android 13+, via android:localeConfig). To add a
+    translation, drop in the values-<tag> folder and add one <locale> line here.
+-->
+<locale-config xmlns:android="http://schemas.android.com/apk/res/android">
+    <locale android:name="en" />
+</locale-config>