feat: implement Android data models in Kotlin

- Add FeedItem, Feed, FeedSubscription models with Moshi JSON support
- Add SearchResult, SearchFilters models with sealed classes for enums
- Add NotificationPreferences, ReadingPreferences models
- Add Room Entity annotations for database readiness
- Add TypeConverters for Date and List<String> serialization
- Add Parcelize for passing models between Activities/Fragments
- Write comprehensive unit tests for serialization/deserialization
- Write tests for copy(), equals/hashCode, and toString functionality

native-route/android/src/main/java/com/rssuper/models/SearchResult.kt

@@ -0,0 +1,49 @@
+package com.rssuper.models
+
+import android.os.Parcelable
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+import androidx.room.TypeConverters
+import com.rssuper.converters.DateConverter
+import kotlinx.parcelize.Parcelize
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+import java.util.Date
+
+@JsonClass(generateAdapter = true)
+@Parcelize
+@TypeConverters(DateConverter::class)
+@Entity(tableName = "search_results")
+data class SearchResult(
+    @PrimaryKey
+    val id: String,
+    
+    @Json(name = "type")
+    val type: SearchResultType,
+    
+    @Json(name = "title")
+    val title: String,
+    
+    @Json(name = "snippet")
+    val snippet: String? = null,
+    
+    @Json(name = "link")
+    val link: String? = null,
+    
+    @Json(name = "feedTitle")
+    val feedTitle: String? = null,
+    
+    @Json(name = "published")
+    val published: Date? = null,
+    
+    @Json(name = "score")
+    val score: Double? = null
+) : Parcelable
+
+enum class SearchResultType {
+    @Json(name = "article")
+    ARTICLE,
+    
+    @Json(name = "feed")
+    FEED
+}