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/AskView.swift

@@ -0,0 +1,152 @@
+import SwiftUI
+
+/// "Ask Your Bookmarks" — the on-device RAG surface. Questions are answered by
+/// Apple's on-device model, grounded in the user's bookmarks via Spotlight.
+struct AskView: View {
+    @State private var assistant = BookmarkAssistant()
+    @State private var question = ""
+    @State private var answer = ""
+    @State private var isLoading = false
+    @State private var errorText: String?
+    @Environment(\.dismiss) private var dismiss
+    @FocusState private var focused: Bool
+
+    var body: some View {
+        NavigationStack {
+            Group {
+                switch assistant.status {
+                case .checking:
+                    ProgressView()
+                case .unavailable(let message):
+                    ContentUnavailableView(
+                        "Unavailable",
+                        systemImage: "sparkles.slash",
+                        description: Text(message)
+                    )
+                case .ready:
+                    ready
+                }
+            }
+            .navigationTitle("Ask Your Bookmarks")
+            .navigationBarTitleDisplayMode(.inline)
+            .toolbar {
+                ToolbarItem(placement: .topBarTrailing) {
+                    Button("Done") { dismiss() }
+                }
+            }
+        }
+    }
+
+    private var ready: some View {
+        VStack(spacing: 0) {
+            ScrollView {
+                VStack(alignment: .leading, spacing: 16) {
+                    if answer.isEmpty && !isLoading && errorText == nil {
+                        ContentUnavailableView {
+                            Label("Ask anything", systemImage: "sparkles")
+                        } description: {
+                            Text("Answers come from your saved bookmarks, generated on-device.")
+                        }
+                        .padding(.top, 40)
+                    }
+                    if isLoading {
+                        HStack(spacing: 8) {
+                            ProgressView()
+                            Text("Searching your bookmarks…").foregroundStyle(.secondary)
+                        }
+                    }
+                    if !answer.isEmpty {
+                        MarkdownAnswer(text: answer)
+                            .textSelection(.enabled)
+                            .frame(maxWidth: .infinity, alignment: .leading)
+                    }
+                    if let errorText {
+                        Text(errorText).foregroundStyle(.red)
+                    }
+                }
+                .padding()
+            }
+
+            HStack(spacing: 10) {
+                TextField("Ask about your bookmarks…", text: $question, axis: .vertical)
+                    .lineLimit(1...4)
+                    .focused($focused)
+                    .submitLabel(.send)
+                    .onSubmit(send)
+                Button(action: send) {
+                    Image(systemName: "arrow.up.circle.fill").font(.title2)
+                }
+                .disabled(question.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty || isLoading)
+            }
+            .padding()
+            .background(.bar)
+        }
+        .onAppear { focused = true }
+    }
+
+    private func send() {
+        let q = question.trimmingCharacters(in: .whitespacesAndNewlines)
+        guard !q.isEmpty, !isLoading else { return }
+        question = ""
+        answer = ""
+        errorText = nil
+        isLoading = true
+        Task {
+            do {
+                answer = try await assistant.ask(q)
+            } catch {
+                errorText = error.localizedDescription
+            }
+            isLoading = false
+        }
+    }
+}
+
+/// Renders the model's answer as lightweight Markdown. SwiftUI's `Text` only
+/// parses *inline* Markdown (bold/italic/code/links), so we split into block
+/// elements — headings, bullet/numbered lists, paragraphs — and lay them out,
+/// applying inline parsing per line.
+private struct MarkdownAnswer: View {
+    let text: String
+
+    private enum Block: Hashable { case heading(String), bullet(String), paragraph(String) }
+
+    var body: some View {
+        VStack(alignment: .leading, spacing: 8) {
+            ForEach(Array(blocks.enumerated()), id: \.offset) { _, block in
+                switch block {
+                case .heading(let line):
+                    inline(line).font(.headline)
+                case .bullet(let line):
+                    HStack(alignment: .firstTextBaseline, spacing: 8) {
+                        Text("•").foregroundStyle(.secondary)
+                        inline(line)
+                    }
+                case .paragraph(let line):
+                    inline(line)
+                }
+            }
+        }
+    }
+
+    private var blocks: [Block] {
+        text.split(separator: "\n", omittingEmptySubsequences: true).map { raw in
+            let line = raw.trimmingCharacters(in: .whitespaces)
+            if let r = line.range(of: "^#{1,6}\\s+", options: .regularExpression) {
+                return .heading(String(line[r.upperBound...]))
+            }
+            if let r = line.range(of: "^([-*+]|\\d+\\.)\\s+", options: .regularExpression) {
+                return .bullet(String(line[r.upperBound...]))
+            }
+            return .paragraph(line)
+        }
+    }
+
+    private func inline(_ s: String) -> Text {
+        let opts = AttributedString.MarkdownParsingOptions(interpretedSyntax: .inlineOnlyPreservingWhitespace)
+        if let attr = try? AttributedString(markdown: s, options: opts) {
+            return Text(attr)
+        }
+        return Text(s)
+    }
+}