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/FeedSubscription.kt

@@ -0,0 +1,63 @@
+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 = "feed_subscriptions")
+data class FeedSubscription(
+    @PrimaryKey
+    val id: String,
+    
+    @Json(name = "url")
+    val url: String,
+    
+    @Json(name = "title")
+    val title: String,
+    
+    @Json(name = "category")
+    val category: String? = null,
+    
+    @Json(name = "enabled")
+    val enabled: Boolean = true,
+    
+    @Json(name = "fetchInterval")
+    val fetchInterval: Long,
+    
+    @Json(name = "createdAt")
+    val createdAt: Date,
+    
+    @Json(name = "updatedAt")
+    val updatedAt: Date,
+    
+    @Json(name = "lastFetchedAt")
+    val lastFetchedAt: Date? = null,
+    
+    @Json(name = "nextFetchAt")
+    val nextFetchAt: Date? = null,
+    
+    @Json(name = "error")
+    val error: String? = null,
+    
+    @Json(name = "httpAuth")
+    val httpAuth: HttpAuth? = null
+) : Parcelable
+
+@JsonClass(generateAdapter = true)
+@Parcelize
+data class HttpAuth(
+    @Json(name = "username")
+    val username: String,
+    
+    @Json(name = "password")
+    val password: String
+) : Parcelable