feat(characters:presentation-compose): list renderer, Root/Screen split, previews (REDI-88)

- CharacterListRoot: koinViewModel(), ObserveAsEvents, forwards nav + shows snackbar via Context asString.
- CharacterListScreen: pure state+onAction; AppScaffold + LazyColumn (key=id), design-system
  NetworkImage (contentDescription)/AppCard, loading/error/empty states, snapshot-based
  scroll-to-end -> OnLoadNextPage (ViewModel guards duplicates).
- Loaded + error previews wrapped in AppTheme.
- feature:characters:presentation now exposes kotlinx-immutable as api (ImmutableList is in the state API).

feature/characters/presentation/build.gradle.kts

@@ -19,5 +19,6 @@ dependencies {
     implementation(libs.kotlinx.coroutines.android)
     // Stable collection for state — makes the list Compose-stable WITHOUT a Compose dependency,
     // so this module stays UI-agnostic (no @Stable annotation, which would require compose-runtime).
-    implementation(libs.kotlinx.collections.immutable)
+    // `api` because CharacterListState.characters exposes ImmutableList in the public state API.
+    api(libs.kotlinx.collections.immutable)
 }