feat: implement cross-platform features and UI integration

- iOS: Add BackgroundSyncService, SyncScheduler, SyncWorker, BookmarkViewModel, FeedViewModel
- iOS: Add BackgroundSyncService, SyncScheduler, SyncWorker services
- Linux: Add settings-store.vala, State.vala signals, view widgets (FeedList, FeedDetail, AddFeed, Search, Settings, Bookmark)
- Linux: Add bookmark-store.vala, bookmark vala model, search-service.vala
- Android: Add NotificationService, NotificationManager, NotificationPreferencesStore
- Android: Add BookmarkDao, BookmarkRepository, SettingsStore
- Add unit tests for iOS, Android, Linux
- Add integration tests
- Add performance benchmarks
- Update tasks and documentation

Co-Authored-By: Paperclip <noreply@paperclip.ing>

native-route/ios/RSSuperTests/SyncWorkerTests.swift

@@ -0,0 +1,64 @@
+import XCTest
+@testable import RSSuper
+
+/// Unit tests for SyncWorker
+final class SyncWorkerTests: XCTestCase {
+    
+    private var worker: SyncWorker!
+    
+    override func setUp() {
+        super.setUp()
+        worker = SyncWorker()
+    }
+    
+    override func tearDown() {
+        worker = nil
+        super.tearDown()
+    }
+    
+    func testChunkedArrayExtension() {
+        let array = [1, 2, 3, 4, 5, 6, 7]
+        let chunks = array.chunked(into: 3)
+        
+        XCTAssertEqual(chunks.count, 3)
+        XCTAssertEqual(chunks[0], [1, 2, 3])
+        XCTAssertEqual(chunks[1], [4, 5, 6])
+        XCTAssertEqual(chunks[2], [7])
+    }
+    
+    func testChunkedArrayExactDivision() {
+        let array = [1, 2, 3, 4]
+        let chunks = array.chunked(into: 2)
+        
+        XCTAssertEqual(chunks.count, 2)
+        XCTAssertEqual(chunks[0], [1, 2])
+        XCTAssertEqual(chunks[1], [3, 4])
+    }
+    
+    func testChunkedArrayEmpty() {
+        let array: [Int] = []
+        let chunks = array.chunked(into: 3)
+        
+        XCTAssertEqual(chunks.count, 0)
+    }
+    
+    func testSyncResultInit() {
+        let result = SyncResult(
+            feedsSynced: 5,
+            articlesFetched: 100,
+            errors: []
+        )
+        
+        XCTAssertEqual(result.feedsSynced, 5)
+        XCTAssertEqual(result.articlesFetched, 100)
+        XCTAssertEqual(result.errors.count, 0)
+    }
+    
+    func testSyncResultDefaultInit() {
+        let result = SyncResult()
+        
+        XCTAssertEqual(result.feedsSynced, 0)
+        XCTAssertEqual(result.articlesFetched, 0)
+        XCTAssertEqual(result.errors.count, 0)
+    }
+}