feat(podcasts): played/unplayed queue, background generation, share-sheet audio

Turns the Podcasts tab into a proper podcast-app experience across three
features that compose on a shared background-generation service.

Background generation (#2)
- New PodcastGenerationManager runs generate→poll→download off the player,
  so producing a new episode never stops current playback.
- Headphone taps never interrupt: idle → generate-and-play in the foreground
  (unchanged); already playing → generate in the background, episode lands in
  the library. A "Generating…" banner surfaces active jobs.

Played/unplayed + queue (#1)
- PodcastEntry gains playedAt (old index.json decodes as unplayed).
- Podcasts tab splits into Up Next / Played with a Play All queue that
  auto-advances; finishing marks played; swipe to toggle played state.

Share-extension audio (#3)
- "Create podcast" toggle on the save card, plus configurable Auto-Podcast
  Tags in Settings. The extension enqueues a request into the App Group; the
  main app drains it on launch/foreground and generates in the background.

Closes #1
Closes #2
Closes #3

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

Marks/Views/BookmarksView.swift

@@ -146,6 +146,10 @@ struct BookmarksView: View {
             }
             .overlay(alignment: .bottom) {
                 VStack(spacing: 8) {
+                    if viewModel.podcastGenerator.hasActive {
+                        podcastGeneratingBanner
+                            .transition(.move(edge: .bottom).combined(with: .opacity))
+                    }
                     if !viewModel.podcastPlayer.currentArticleUrl.isEmpty {
                         MiniPlayerView(vm: viewModel.podcastPlayer) {
                             showFullPlayer = true
@@ -157,6 +161,7 @@ struct BookmarksView: View {
                     }
                 }
                 .animation(.spring(duration: 0.3), value: !viewModel.podcastPlayer.currentArticleUrl.isEmpty)
+                .animation(.spring(duration: 0.3), value: viewModel.podcastGenerator.hasActive)
                 .padding(.bottom, 8)
             }
             .sensoryFeedback(.selection, trigger: browsingBookmark?.id)
@@ -178,7 +183,7 @@ struct BookmarksView: View {
         }
         .sheet(item: $browsingBookmark) { bookmark in
             if let url = URL(string: bookmark.url) {
-                BrowserView(url: url, title: bookmark.displayTitle, claude: viewModel.claude, podcastPlayer: viewModel.podcastPlayer) {
+                BrowserView(url: url, title: bookmark.displayTitle, claude: viewModel.claude, podcastPlayer: viewModel.podcastPlayer, podcastGenerator: viewModel.podcastGenerator) {
                     await viewModel.archive(bookmark)
                 }
                 .bookmarkOnscreen(bookmark)
@@ -230,6 +235,40 @@ struct BookmarksView: View {
         .padding(.horizontal, 16)
     }
 
+    private var podcastGeneratingBanner: some View {
+        let jobs = viewModel.podcastGenerator.activeJobs
+        return HStack(spacing: 10) {
+            Image(systemName: "waveform")
+                .font(.system(size: 15, weight: .semibold))
+                .foregroundStyle(.blue)
+                .symbolEffect(.variableColor.iterative, isActive: true)
+            VStack(alignment: .leading, spacing: 2) {
+                Text(jobs.count == 1 ? "Generating podcast…" : "Generating \(jobs.count) podcasts…")
+                    .font(.system(size: 13, weight: .medium))
+                if let first = jobs.first {
+                    Text(first.title.isEmpty ? first.label : first.title)
+                        .font(.system(size: 11))
+                        .foregroundStyle(.secondary)
+                        .lineLimit(1)
+                }
+            }
+            Spacer()
+            if jobs.count == 1, let progress = jobs.first?.progress, progress > 0 {
+                ProgressView(value: progress)
+                    .progressViewStyle(.linear)
+                    .tint(.blue)
+                    .frame(width: 44)
+            } else {
+                ProgressView()
+            }
+        }
+        .padding(.horizontal, 16)
+        .padding(.vertical, 10)
+        .background(.regularMaterial)
+        .clipShape(RoundedRectangle(cornerRadius: 12))
+        .padding(.horizontal, 16)
+    }
+
     private func maybeLoadMore(_ bookmark: Bookmark) {
         guard let last = viewModel.bookmarks.last, last.id == bookmark.id,
               viewModel.nextPageUrl != nil, !viewModel.isLoadingMore else { return }