feat(characters): Koin module + nav graph + wire into :app (REDI-89)

- charactersPresentationModule: viewModelOf(::CharacterListViewModel) (in the UI-agnostic module).
- @Serializable CharacterListRoute + NavGraphBuilder.charactersGraph { composable<CharacterListRoute> }
  in presentation-compose (serialization plugin added for type-safe routes).
- :app registers coreDataModule + charactersDataModule + charactersPresentationModule in startKoin,
  and hosts a NavHost(startDestination = CharacterListRoute) calling charactersGraph.
- core:data manifest declares INTERNET (merges into :app) for live API calls.

feature/characters/presentation-compose/build.gradle.kts

@@ -1,5 +1,7 @@
 plugins {
     alias(libs.plugins.architecture.android.feature)
+    // For @Serializable type-safe navigation routes.
+    alias(libs.plugins.architecture.kotlinx.serialization)
 }
 
 android {

feature/characters/presentation-compose/src/main/kotlin/com/example/architecture/feature/characters/presentation/compose/CharactersNavigation.kt

@@ -0,0 +1,21 @@
+package com.example.architecture.feature.characters.presentation.compose
+
+import androidx.navigation.NavGraphBuilder
+import androidx.navigation.compose.composable
+import kotlinx.serialization.Serializable
+
+/** Type-safe route for the characters list screen. */
+@Serializable
+data object CharacterListRoute
+
+/**
+ * The characters feature nav graph. `:app` only calls this and supplies cross-screen navigation as
+ * a callback. The detail destination is added here in a later milestone.
+ */
+fun NavGraphBuilder.charactersGraph(
+    onCharacterClick: (Int) -> Unit,
+) {
+    composable<CharacterListRoute> {
+        CharacterListRoot(onCharacterClick = onCharacterClick)
+    }
+}