fix: Dynamic Island, Live Activity errors, background audio stop, CFBundleVersion

Phase 1 — Audio background resilience:
- Remove .mixWithOthers, app takes audio focus for coach cues
- Add AVAudioSession.interruptionNotification handler (re-activates after calls/Siri)
- Add AVAudioSession.routeChangeNotification handler (re-activates on headphone changes)

Phase 2 — Live Activity error surfacing:
- PlayerViewModel: @Published liveActivityError captures auth-denied + request errors
- PlayerView: translucent error banner with dismiss button (non-blocking)

Phase 3 — CFBundleVersion 1→2 in all 4 Info.plist files (match project.yml CURRENT_PROJECT_VERSION: 2)

tabatago-swift/TabataGo/Views/Player/PlayerView.swift

@@ -66,6 +66,40 @@ struct PlayerView: View {
                     }
                 }
 
+                // ══════════════════════════════════════════════════
+                // Live Activity error banner (non-blocking)
+                // ══════════════════════════════════════════════════
+                if let error = vm.liveActivityError {
+                    VStack {
+                        HStack(spacing: 8) {
+                            Image(systemName: "exclamationmark.triangle.fill")
+                                .font(.caption)
+                                .foregroundStyle(.yellow)
+                            Text(error)
+                                .font(.caption2.weight(.medium))
+                                .foregroundStyle(.white.opacity(0.9))
+                            Spacer()
+                            Button {
+                                vm.liveActivityError = nil
+                            } label: {
+                                Image(systemName: "xmark")
+                                    .font(.system(size: 10, weight: .bold))
+                                    .foregroundStyle(.white.opacity(0.6))
+                            }
+                        }
+                        .padding(.horizontal, 16)
+                        .padding(.vertical, 10)
+                        .background(.ultraThinMaterial.opacity(0.9))
+                        .clipShape(RoundedRectangle(cornerRadius: 12))
+                        .padding(.horizontal, 16)
+                        .padding(.top, 60)
+                        Spacer()
+                    }
+                    .transition(.move(edge: .top).combined(with: .opacity))
+                    .animation(.spring(duration: 0.3), value: vm.liveActivityError)
+                    .zIndex(100)
+                }
+
                 // ══════════════════════════════════════════════════
                 // Layer 4 — Compact timer ring (top-right corner)
                 // ══════════════════════════════════════════════════