feat(ai): on-device RAG over bookmarks + Spotlight indexing + unified logging

- SpotlightIndexer: actually push BookmarkEntity into the Spotlight index via
  indexAppEntities (IndexedEntity conformance alone indexes nothing). Wired into
  every sync/mutation point. This is what lets Apple Intelligence answer
  free-form Siri questions grounded in the user's bookmarks.
- On-device RAG: BookmarkAssistant (LanguageModelSession) + BookmarkSearchTool
  + SpotlightBookmarkSearch (CSSearchQuery retrieval), surfaced via AskView with
  lightweight Markdown rendering of answers.
- Log: os.Logger facility (com.magicive.marks) replacing ad-hoc print(); shared
  with ShareExtension. ClaudeService now logs server error bodies on non-2xx.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Marks/Views/BookmarksView.swift

@@ -59,6 +59,7 @@ struct BookmarksView: View {
     @State private var browsingBookmark: Bookmark?
     @State private var showFullPlayer = false
     @State private var showPodcastLibrary = false
+    @State private var showAsk = false
     @State private var readingProgress: [String: Double] = ReadingProgress.all()
 
     var body: some View {
@@ -95,6 +96,11 @@ struct BookmarksView: View {
             .toolbar {
                 ToolbarItem(placement: .topBarLeading) {
                     Menu {
+                        Button {
+                            showAsk = true
+                        } label: {
+                            Label("Ask Your Bookmarks", systemImage: "bubble.left.and.text.bubble.right")
+                        }
                         Button {
                             Task { await viewModel.generateSmartCollections() }
                             showCollections = true
@@ -167,6 +173,9 @@ struct BookmarksView: View {
         .sheet(isPresented: $showCollections) {
             CollectionsView(viewModel: viewModel)
         }
+        .sheet(isPresented: $showAsk) {
+            AskView()
+        }
         .sheet(isPresented: $showAddBookmark) {
             AddBookmarkView(viewModel: viewModel)
         }