Add mini-player, per-row podcast button, and resume-from-position

- MiniPlayerView: persistent bar above tab bar, shows title/progress,
  play/pause and close buttons, slides in when audio starts
- PodcastPlayerViewModel lifted to BookmarksViewModel so it persists
  across sheet dismissals — audio keeps playing in background
- Headphone button on every bookmark row (filled = cached, outline = not)
- start() is idempotent: re-tapping same article resumes without restart
- stop() saves playback position before teardown (PodcastProgress)
- setupPlayer restores saved position on next open
- BrowserView keeps its own local VM (stopOnDismiss: true)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Marks/Views/BrowserView.swift

@@ -202,6 +202,7 @@ struct BrowserView: View {
     @State private var state: BrowserState
     @State private var readerMode = false
     @State private var showPodcast = false
+    @State private var podcastVM = PodcastPlayerViewModel()
 
     init(url: URL, title: String, claude: ClaudeService) {
         self.initialURL = url
@@ -290,7 +291,13 @@ struct BrowserView: View {
             if p > 0.01 { ReadingProgress.set(url: urlStr, progress: p) }
         }
         .sheet(isPresented: $showPodcast) {
-            PodcastPlayerView(articleUrl: (state.currentURL ?? initialURL).absoluteString, claude: claude)
+            PodcastPlayerView(
+                vm: podcastVM,
+                articleUrl: (state.currentURL ?? initialURL).absoluteString,
+                articleTitle: state.pageTitle.isEmpty ? initialTitle : state.pageTitle,
+                claude: claude,
+                stopOnDismiss: true
+            )
         }
     }
 }