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>

.gitignore

@@ -1,50 +1,25 @@
-# Miscellaneous
-*.class
-*.log
-*.pyc
-*.swp
-.DS_Store
-.atom/
+# Xcode user data
+xcuserdata/
+*.xcuserstate
+
+# Build artifacts
+DerivedData/
+build/
+*.ipa
+*.dSYM.zip
+*.dSYM
+
+# Swift Package Manager
 .build/
-.buildlog/
-.history
-.svn/
 .swiftpm/
-migrate_working_dir/
 
-# IntelliJ related
-*.iml
-*.ipr
-*.iws
-.idea/
+# CocoaPods
+Pods/
 
-# The .vscode folder contains launch configuration and tasks you configure in
-# VS Code which you may wish to be included in version control, so this line
-# is commented out by default.
-#.vscode/
+# macOS
+.DS_Store
+.DS_Store?
+._*
 
-# Flutter/Dart/Pub related
-**/doc/api/
-**/ios/Flutter/.last_build_id
-.dart_tool/
-.flutter-plugins
-.flutter-plugins-dependencies
-.pub-cache/
-.pub/
-/build/
-
-# Symbolication related
-app.*.symbols
-
-# Obfuscation related
-app.*.map.json
-
-# Android Studio will place build artifacts here
-/android/app/debug
-/android/app/profile
-/android/app/release
-
-# Env file
-.env
-android/app/.cxx
-android/build/reports/problems
+# VS Code
+.vscode/