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/Models/Bookmark.swift

@@ -0,0 +1,73 @@
+import Foundation
+
+struct Bookmark: Codable, Identifiable, Sendable, Hashable {
+    let id: Int
+    var url: String
+    var title: String
+    var description: String
+    var tagNames: [String]
+    var dateAdded: Date
+    var dateModified: Date
+    var isArchived: Bool
+    var unread: Bool
+    var shared: Bool
+    var websiteTitle: String?
+    var websiteDescription: String?
+    var faviconUrl: String?
+    var previewImageUrl: String?
+
+    // AI-enriched fields stored locally
+    var aiSummary: String?
+    var aiTags: [String]?
+
+    enum CodingKeys: String, CodingKey {
+        case id, url, title, description, unread, shared
+        case tagNames = "tag_names"
+        case dateAdded = "date_added"
+        case dateModified = "date_modified"
+        case isArchived = "is_archived"
+        case websiteTitle = "website_title"
+        case websiteDescription = "website_description"
+        case faviconUrl = "favicon_url"
+        case previewImageUrl = "preview_image_url"
+    }
+
+    var displayTitle: String {
+        if !title.isEmpty { return title }
+        if let t = websiteTitle, !t.isEmpty { return t }
+        return url
+    }
+
+    var domain: String {
+        URL(string: url)?.host ?? url
+    }
+}
+
+struct BookmarkResponse: Codable, Sendable {
+    let count: Int
+    let next: String?
+    let previous: String?
+    let results: [Bookmark]
+}
+
+struct BookmarkCreate: Codable, Sendable {
+    let url: String
+    let title: String
+    let tagNames: [String]
+    let isArchived: Bool
+    let unread: Bool
+    let shared: Bool
+
+    enum CodingKeys: String, CodingKey {
+        case url, title, unread, shared
+        case tagNames = "tag_names"
+        case isArchived = "is_archived"
+    }
+}
+
+struct SmartCollection: Identifiable, Sendable {
+    let id = UUID()
+    let name: String
+    let description: String
+    let bookmarkIds: [Int]
+}