M2: wire navigation host + base screen scaffolds

Replace the RootScreen nav stubs with a real NavHost. Each destination
binds its existing M1 ViewModel from route args.

- ui/navigation: Dest route table (string-based; no serialization plugin)
  + FloretNavHost (lists -> task list -> detail / edit).
- Base scaffolds for TaskListScreen, TaskDetailScreen, TaskEditScreen,
  wired to their ViewModels — skeletons for the rich M2/M3 UI.
- RootScreen READY branch now hands off to FloretNavHost.
- Add navigation-compose 2.9.0; supporting strings.

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

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

@@ -4,6 +4,28 @@
 
     <!-- Generic -->
     <string name="task_untitled">Untitled task</string>
+    <string name="back">Back</string>
+    <string name="save">Save</string>
+    <string name="delete">Delete</string>
+
+    <!-- Task list -->
+    <string name="tasks_title">Tasks</string>
+    <string name="task_list_empty">No tasks here yet.</string>
+    <string name="task_list_failure">Could not load these tasks.</string>
+    <string name="smart_no_date">No date</string>
+    <string name="smart_completed">Completed</string>
+
+    <!-- Task detail -->
+    <string name="task_detail_title">Task</string>
+    <string name="task_detail_not_found">This task no longer exists.</string>
+    <string name="edit">Edit</string>
+
+    <!-- Task edit -->
+    <string name="edit_task_title">Edit task</string>
+    <string name="new_task_title">New task</string>
+    <string name="field_title">Title</string>
+    <string name="field_description">Description</string>
+    <string name="edit_save_failed">Could not save. Try again.</string>
 
     <!-- Lists overview -->
     <string name="lists_header">Lists</string>