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/settings.gradle.kts

@@ -0,0 +1,18 @@
+pluginManagement {
+    repositories {
+        google()
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
+
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+
+rootProject.name = "native-route"
+include(":android")