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/build.gradle.kts

@@ -110,6 +110,7 @@ dependencies {
 
     implementation(libs.hilt.android)
     implementation(libs.androidx.hilt.navigation.compose)
+    implementation(libs.androidx.navigation.compose)
     ksp(libs.hilt.compiler)
 
     implementation(libs.androidx.datastore.preferences)