experiment(PodcastPlayerView): add skip ±15s buttons to full player controls

Marks/Views/PodcastPlayerView.swift

@@ -144,6 +144,14 @@ final class PodcastPlayerViewModel {
         updateNowPlaying()
     }
 
+    func skipForward15() {
+        seek(to: min(currentTime + 15, duration))
+    }
+
+    func skipBackward15() {
+        seek(to: max(currentTime - 15, 0))
+    }
+
     private func setupPlayer(url: URL, title: String) {
         currentPodcastTitle = title
 
@@ -347,11 +355,23 @@ struct PodcastPlayerView: View {
                 .foregroundStyle(.tertiary)
             }
 
+            HStack(spacing: 36) {
+                Button { vm.skipBackward15() } label: {
+                    Image(systemName: "gobackward.15")
+                        .font(.system(size: 32))
+                        .foregroundStyle(.primary)
+                }
                 Button { vm.togglePlayPause() } label: {
                     Image(systemName: vm.isPlaying ? "pause.circle.fill" : "play.circle.fill")
                         .font(.system(size: 72))
                         .foregroundStyle(.primary)
                 }
+                Button { vm.skipForward15() } label: {
+                    Image(systemName: "goforward.15")
+                        .font(.system(size: 32))
+                        .foregroundStyle(.primary)
+                }
+            }
         }
     }