feat(podcasts): add a Podcasts tab to list and play on demand

Surface every podcast in PodcastIndex as a top-level tab instead of a
buried sheet. Repurpose PodcastLibraryView into the tab: play/pause toggle
per episode, a now-playing bar that opens the full player, swipe/Edit to
delete. Uses the shared podcastPlayer so playback state is consistent
across tabs. Removes the redundant Podcasts entry from the bookmarks menu.

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

Marks/Views/BookmarksView.swift

@@ -58,7 +58,6 @@ struct BookmarksView: View {
     @State private var editingBookmark: Bookmark?
     @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()
 
@@ -112,11 +111,6 @@ struct BookmarksView: View {
                         } label: {
                             Label("Enrich All with AI", systemImage: "wand.and.stars")
                         }
-                        Button {
-                            showPodcastLibrary = true
-                        } label: {
-                            Label("Podcasts", systemImage: "headphones")
-                        }
                     } label: {
                         Image(systemName: "sparkles")
                     }
@@ -202,9 +196,6 @@ struct BookmarksView: View {
                 stopOnDismiss: false
             )
         }
-        .sheet(isPresented: $showPodcastLibrary) {
-            PodcastLibraryView(vm: viewModel.podcastPlayer, claude: viewModel.claude)
-        }
         .refreshable {
             await viewModel.load()
         }