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/FeedItem.kt

@@ -0,0 +1,67 @@
+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 com.rssuper.converters.StringListConverter
+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, StringListConverter::class)
+@Entity(tableName = "feed_items")
+data class FeedItem(
+    @PrimaryKey
+    val id: String,
+    
+    @Json(name = "title")
+    val title: String,
+    
+    @Json(name = "link")
+    val link: String? = null,
+    
+    @Json(name = "description")
+    val description: String? = null,
+    
+    @Json(name = "content")
+    val content: String? = null,
+    
+    @Json(name = "author")
+    val author: String? = null,
+    
+    @Json(name = "published")
+    val published: Date? = null,
+    
+    @Json(name = "updated")
+    val updated: Date? = null,
+    
+    @Json(name = "categories")
+    val categories: List<String>? = null,
+    
+    @Json(name = "enclosure")
+    val enclosure: Enclosure? = null,
+    
+    @Json(name = "guid")
+    val guid: String? = null,
+    
+    @Json(name = "subscriptionTitle")
+    val subscriptionTitle: String? = null
+) : Parcelable
+
+@JsonClass(generateAdapter = true)
+@Parcelize
+data class Enclosure(
+    @Json(name = "url")
+    val url: String,
+    
+    @Json(name = "type")
+    val type: String,
+    
+    @Json(name = "length")
+    val length: Long? = null
+) : Parcelable