feat: implement Android database layer with Room

- Add SubscriptionEntity, FeedItemEntity, SearchHistoryEntity
- Create SubscriptionDao, FeedItemDao, SearchHistoryDao with CRUD operations
- Implement RssDatabase with FTS5 virtual table for full-text search
- Add type converters for Date, String lists, and FeedItem lists
- Implement cascade delete for feed items when subscription is removed
- Add comprehensive unit tests for all DAOs
- Add database integration tests for entity round-trips and FTS
- Configure Room testing dependencies

native-route/android/build.gradle.kts

@@ -48,4 +48,10 @@ dependencies {
     testImplementation("com.squareup.moshi:moshi-kotlin-reflect:1.15.1")
     testImplementation("org.mockito:mockito-core:5.7.0")
     testImplementation("org.mockito:mockito-inline:5.2.0")
+    testImplementation("androidx.room:room-testing:2.6.1")
+    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.7.3")
+    testImplementation("androidx.arch.core:core-testing:2.2.0")
+    testImplementation("androidx.test:core:1.5.0")
+    testImplementation("androidx.test.ext:junit:1.1.5")
+    testImplementation("androidx.test:runner:1.5.2")
 }