M1: full task data layer, reminders and ViewModels over OpenTasks

Non-visual stack (backoffice) complete and verified against the real
provider semantics (tasks.org's bundled dmfs TaskProvider, authority
org.tasks.opentasks, org.tasks.permission.* dangerous):

- TaskContract subset + ProviderResolver (runtime authority/permission)
- AndroidTasksDataSource (Instances query, ContentObserver) + TasksRepository
  with live Flows; domain models, smart-list filtering, sorting, form validation
- Self-scheduled due-reminder engine (AlarmManager, boot/provider-change)
- Render-only ViewModels + UiState for every screen
- 24 JVM unit tests; assembleDebug + lintDebug + testDebugUnitTest green
- RootScreen is a functional scaffold over real data, to be replaced with the
  Material 3 Expressive screens one by one

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

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

@@ -1,4 +1,21 @@
 <resources>
     <string name="app_name">Floret</string>
     <string name="app_tagline">A modern Material 3 Expressive task app.\nComing into bloom.</string>
+
+    <!-- Generic -->
+    <string name="task_untitled">Untitled task</string>
+
+    <!-- Reminders -->
+    <string name="reminder_due_at">Due %1$s</string>
+    <string name="reminder_channel_name">Task reminders</string>
+    <string name="reminder_channel_desc">Notifications for tasks that are due.</string>
+
+    <!-- Provider / permission onboarding -->
+    <string name="onboarding_no_provider_title">A tasks app is needed</string>
+    <string name="onboarding_no_provider_body">Floret shows and edits the tasks stored by OpenTasks or tasks.org, synced by DAVx5. Install one of them to get started.</string>
+    <string name="onboarding_permission_title">Allow access to your tasks</string>
+    <string name="onboarding_permission_body">Floret needs permission to read and write your tasks. That\'s the only thing it ever asks for.</string>
+    <string name="onboarding_permission_button">Grant task access</string>
+    <string name="onboarding_install_opentasks">Install OpenTasks</string>
+    <string name="onboarding_install_tasksorg">Install tasks.org</string>
 </resources>