feat(backend): Phase 2.1 scaffolding for bookshelf-api + ABS

- Port BookshelfApiService, AudiobookshelfApiService and all models from Book's Story.
- Add Hilt 2.56.1 plugin, @HiltAndroidApp, NetworkModule, BackendModule.
- Add Retrofit/OkHttp/Kotlinx Serialization dependencies.
- Provide minimal SharedPreferences-based ServerSettings for URL/token storage.
- Copy UriUtils (fixUriScheme/normalizeUri) from Book's Story.
- No wiring into UI yet; OPDS/Gutenberg/LocalFolder still present.
- ':app:assembleOssDebug' passes (APK ~80 MB).

app/build.gradle.kts

@@ -11,6 +11,7 @@ plugins {
     alias(libs.plugins.kotlin.compose)
     alias(libs.plugins.kotlin.serialization)
     alias(libs.plugins.kotlin.ksp)
+    alias(libs.plugins.hilt)
     id("com.diffplug.spotless") version "8.2.1"
     alias(libs.plugins.kover)
 }
@@ -228,6 +229,16 @@ dependencies {
     implementation(libs.androidx.material3.window.size.class1.android)
     implementation(libs.androidx.credentials)
 
+    // Hilt
+    implementation(libs.hilt.android)
+    ksp(libs.hilt.compiler)
+    implementation(libs.hilt.navigation.compose)
+
+    // Networking
+    implementation(libs.retrofit)
+    implementation(libs.retrofit.kotlinx.serialization)
+    implementation(libs.okhttp.logging)
+
     androidTestImplementation(libs.androidx.junit)
     androidTestImplementation(libs.androidx.espresso.core)
     androidTestImplementation(platform(libs.androidx.compose.bom))