feat(intents): add App Intents + Siri integration

Expose Marks to Siri, Spotlight, and Shortcuts via App Intents:

- BookmarkEntity (AppEntity + IndexedEntity, keyed on the Linkding
  server id) with a server-backed EntityStringQuery for live lookup
- Intents: Add, Open (OpenIntent), Search, ShowUnread, and an AI
  Summarize intent backed by ClaudeService; AppShortcutsProvider with
  spoken phrases; Siri snippet views and dialog
- SearchMarksIntent conforms to the system.search App Schema
  (@AppIntent(schema:), ShowInAppSearchResultsIntent) so it is
  executable by conversational Siri / Apple Intelligence
- IntentRouter bridges intents (run in the app process) to the SwiftUI
  scene for open/search navigation; widgets refreshed after adds
- Link AppIntents.framework so the metadata processor extracts shortcut
  phrases and validates the assistant schema

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Marks/MarksApp.swift

@@ -36,6 +36,8 @@ struct MainContainer: View {
     @State private var viewModel: BookmarksViewModel
     @State private var deepLinkBrowser: IdentifiableURL?
     @State private var showDeepLinkPlayer = false
+    @State private var selectedTab: AppTab = .bookmarks
+    @State private var router = IntentRouter.shared
 
     init(config: ServerConfig, onDisconnect: @escaping () -> Void) {
         self.config = config
@@ -45,20 +47,23 @@ struct MainContainer: View {
     }
 
     var body: some View {
-        TabView {
-            Tab("Bookmarks", systemImage: "bookmark") {
+        TabView(selection: $selectedTab) {
+            Tab("Bookmarks", systemImage: "bookmark", value: AppTab.bookmarks) {
                 BookmarksView(viewModel: viewModel, onDisconnect: onDisconnect)
             }
-            Tab("Tags", systemImage: "tag") {
+            Tab("Tags", systemImage: "tag", value: AppTab.tags) {
                 TagsView(viewModel: viewModel)
             }
-            Tab(role: .search) {
+            Tab(value: AppTab.search, role: .search) {
                 SearchView(viewModel: viewModel)
             }
         }
         .onOpenURL { url in
             handleDeepLink(url)
         }
+        .task { applyPendingIntent() }
+        .onChange(of: router.openBookmarkURL) { _, _ in applyPendingIntent() }
+        .onChange(of: router.searchRequest) { _, _ in applyPendingIntent() }
         .sheet(item: $deepLinkBrowser) { item in
             BrowserView(url: item.url, title: item.url.host ?? "", claude: viewModel.claude, podcastPlayer: viewModel.podcastPlayer)
         }
@@ -73,6 +78,27 @@ struct MainContainer: View {
         }
     }
 
+    /// Reacts to requests an App Intent placed on `IntentRouter` (opening a
+    /// bookmark, or searching). Also runs once at launch so cold-starts via an
+    /// intent are honored.
+    private func applyPendingIntent() {
+        if let urlString = router.openBookmarkURL {
+            router.openBookmarkURL = nil
+            if let url = URL(string: urlString) {
+                deepLinkBrowser = IdentifiableURL(url: url)
+            }
+        }
+        if let query = router.searchRequest {
+            selectedTab = .search
+            Task {
+                viewModel.searchQuery = query
+                await viewModel.search()
+            }
+            // SearchView consumes the text from the router on appear; leave it
+            // set until then, then SearchView clears it.
+        }
+    }
+
     private func handleDeepLink(_ url: URL) {
         guard url.scheme == "marks",
               let comps = URLComponents(url: url, resolvingAgainstBaseURL: false),