Replace Flutter app with native SwiftUI rewrite (iOS 26)

Complete ground-up rewrite in SwiftUI targeting iOS 26. Drops the Flutter/Dart
codebase entirely in favour of a lean native app with no third-party dependencies.

Features shipped:
- Bookmark list with pagination, pull-to-refresh, swipe delete/archive
- Add bookmark form + iOS share extension (zero-tap save from any app)
- Tags tab — all tags sorted by count, tap to browse filtered bookmarks
- Native search tab (Tab role: .search) with instant client-side filtering
- AI enrichment via OpenRouter (google/gemini-2.0-flash-lite-001): auto-summary
  and tag generation, semantic search, smart collections
- Settings: linkding server config, OpenRouter API key
- App Groups for credential sharing between main app and share extension
- Swift 6 strict concurrency throughout (@Observable, @MainActor)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Marks/MarksApp.swift

@@ -0,0 +1,52 @@
+import SwiftUI
+
+@main
+struct MarksApp: App {
+    @State private var serverConfig: ServerConfig? = ServerConfig.load()
+
+    var body: some Scene {
+        WindowGroup {
+            if let config = serverConfig {
+                MainContainer(config: config) {
+                    config.delete()
+                    serverConfig = nil
+                }
+            } else {
+                OnboardingView { newConfig in
+                    newConfig.save()
+                    serverConfig = newConfig
+                }
+            }
+        }
+    }
+}
+
+// Holds the API + ViewModel so they survive re-renders
+struct MainContainer: View {
+    let config: ServerConfig
+    let onDisconnect: () -> Void
+
+    @State private var viewModel: BookmarksViewModel
+
+    init(config: ServerConfig, onDisconnect: @escaping () -> Void) {
+        self.config = config
+        self.onDisconnect = onDisconnect
+        let api = LinkdingAPI(config: config)
+        let claude = ClaudeService.load()
+        _viewModel = State(wrappedValue: BookmarksViewModel(api: api, claude: claude))
+    }
+
+    var body: some View {
+        TabView {
+            Tab("Bookmarks", systemImage: "bookmark") {
+                BookmarksView(viewModel: viewModel, onDisconnect: onDisconnect)
+            }
+            Tab("Tags", systemImage: "tag") {
+                TagsView(viewModel: viewModel)
+            }
+            Tab(role: .search) {
+                SearchView(viewModel: viewModel)
+            }
+        }
+    }
+}