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>

gradle/libs.versions.toml

@@ -22,6 +22,7 @@ kotlinxDatetime = "0.7.0"
 kotlinxCoroutines = "1.10.2"
 turbine = "1.2.0"
 hiltNavigationCompose = "1.3.0"
+navigationCompose = "2.9.0"
 lifecycleCompose = "2.10.0"
 androidxTestRules = "1.7.0"
 # Glance: 1.1.1 is the latest stable (1.2.0 is still rc, 1.3.0 alpha).
@@ -78,6 +79,9 @@ turbine = { group = "app.cash.turbine", name = "turbine", version.ref = "turbine
 # Hilt navigation-compose (for hiltViewModel() in Composables)
 androidx-hilt-navigation-compose = { group = "androidx.hilt", name = "hilt-navigation-compose", version.ref = "hiltNavigationCompose" }
 
+# Navigation-compose (the NavHost / back stack)
+androidx-navigation-compose = { group = "androidx.navigation", name = "navigation-compose", version.ref = "navigationCompose" }
+
 # Lifecycle compose (for collectAsStateWithLifecycle)
 androidx-lifecycle-runtime-compose = { group = "androidx.lifecycle", name = "lifecycle-runtime-compose", version.ref = "lifecycleCompose" }