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/build.gradle.kts

@@ -0,0 +1,5 @@
+plugins {
+    id("com.android.application") version "8.2.0" apply false
+    id("com.android.library") version "8.2.0" apply false
+    id("org.jetbrains.kotlin.android") version "1.9.20" apply false
+}