feat: production-grade Live Activity with type-safe phases, decomposed views, previews, and alert transitions

- Replace raw string phase model with WorkoutPhase enum (Codable, Sendable, CaseIterable)
  with built-in .capitalized display name and SwiftUI .color per phase
- Decompose WorkoutLiveActivity into reusable view structs: PhasePill, CountdownText,
  WorkoutProgressBar, MusicInfoRow, HeartRateBadge, PhaseIndicatorDot, WorkoutLockScreenView,
  WorkoutSmallView — following CraftingSwift iOS 26 architecture patterns
- Add AlertConfiguration on work/rest/complete phase transitions so Dynamic Island
  expands and lights up at key moments
- Add 13 #Preview blocks across both widgets covering all presentation types:
  lock screen, expanded, compact, minimal — for instant Xcode Canvas feedback
- Add stale state handling (context.isStale shows 'Last updated' indicator)
- MusicLiveActivity: 5 new #Preview blocks for playing/paused/expanded/compact/minimal

tabatago-swift/TabataGoWidget/MusicLiveActivity.swift

@@ -186,3 +186,36 @@ struct LiveActivityMusicBars: View {
 private let barMaxHeights: [CGFloat] = [8, 14, 6, 12]
 private let barMin: CGFloat = 3
 private let barSpeeds: [Double] = [2.2, 1.8, 2.8, 1.5]
+
+// MARK: - Previews
+
+#Preview("Lock Screen — Playing", as: .content, using: MusicActivityAttributes()) {
+    MusicLiveActivity()
+} contentStates: {
+    MusicActivityAttributes.ContentState(title: "Lose Yourself", artist: "Eminem", isPlaying: true)
+}
+
+#Preview("Lock Screen — Paused", as: .content, using: MusicActivityAttributes()) {
+    MusicLiveActivity()
+} contentStates: {
+    MusicActivityAttributes.ContentState(title: "Stronger", artist: "Kanye West", isPlaying: false)
+}
+
+#Preview("Dynamic Island Expanded", as: .dynamicIsland(.expanded), using: MusicActivityAttributes()) {
+    MusicLiveActivity()
+} contentStates: {
+    MusicActivityAttributes.ContentState(title: "Till I Collapse", artist: "Eminem", isPlaying: true)
+    MusicActivityAttributes.ContentState(title: "Eye of the Tiger", artist: "Survivor", isPlaying: false)
+}
+
+#Preview("Dynamic Island Compact", as: .dynamicIsland(.compact), using: MusicActivityAttributes()) {
+    MusicLiveActivity()
+} contentStates: {
+    MusicActivityAttributes.ContentState(title: "Lose Yourself", artist: "Eminem", isPlaying: true)
+}
+
+#Preview("Dynamic Island Minimal", as: .dynamicIsland(.minimal), using: MusicActivityAttributes()) {
+    MusicLiveActivity()
+} contentStates: {
+    MusicActivityAttributes.ContentState(title: "Lose Yourself", artist: "Eminem", isPlaying: true)
+}