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/TabataGo/ViewModels/PlayerViewModel.swift

@@ -371,10 +371,11 @@ final class PlayerViewModel: ObservableObject {
 
         let isPlayingMusic = (phase == .work || phase == .rest) && isRunning && !isPaused
         let phaseEnd = Date().addingTimeInterval(Double(timeRemaining))
+        let workoutPhase = WorkoutPhase(rawValue: phase.rawValue) ?? .prep
 
         let state = WorkoutActivityAttributes.ContentState(
             exerciseName: currentExercise?.nameEn ?? "",
-            phase: phase.rawValue,
+            phase: workoutPhase,
             phaseEndDate: phaseEnd,
             roundCurrent: currentRound,
             roundTotal: totalRoundsInBlock,
@@ -385,7 +386,6 @@ final class PlayerViewModel: ObservableObject {
             isPaused: isPaused
         )
 
-        // Discard stale reference — user may have dismissed the Dynamic Island
         if let existing = workoutActivity, existing.activityState != .active {
             workoutActivity = nil
         }
@@ -393,14 +393,32 @@ final class PlayerViewModel: ObservableObject {
         if let existing = workoutActivity {
             nonisolated(unsafe) let safeExisting = existing
             let staleDate = Date().addingTimeInterval(isPaused ? 3600 : 120)
+            let alert = alertForPhase(workoutPhase)
             Task { @MainActor in
-                await safeExisting.update(ActivityContent(state: state, staleDate: staleDate))
+                if let alert {
+                    await safeExisting.update(ActivityContent(state: state, staleDate: staleDate), alertConfiguration: alert)
+                } else {
+                    await safeExisting.update(ActivityContent(state: state, staleDate: staleDate))
+                }
             }
         } else {
             createOrUpdateActivity(with: state)
         }
     }
 
+    private func alertForPhase(_ phase: WorkoutPhase) -> AlertConfiguration? {
+        switch phase {
+        case .work:
+            return AlertConfiguration(title: "Work!", body: "Round \(currentRound) of \(totalRoundsInBlock)", sound: .default)
+        case .rest:
+            return AlertConfiguration(title: "Rest", body: "Recover before the next round", sound: .default)
+        case .complete:
+            return AlertConfiguration(title: "Workout Complete!", body: "Great job!", sound: .default)
+        default:
+            return nil
+        }
+    }
+
     private func createOrUpdateActivity(with state: WorkoutActivityAttributes.ContentState) {
         let attrs = WorkoutActivityAttributes()
         do {
@@ -424,7 +442,7 @@ final class PlayerViewModel: ObservableObject {
         guard safeActivity.activityState == .active else { return }
         let finalState = WorkoutActivityAttributes.ContentState(
             exerciseName: safeActivity.content.state.exerciseName,
-            phase: "complete",
+            phase: .complete,
             phaseEndDate: safeActivity.content.state.phaseEndDate,
             roundCurrent: safeActivity.content.state.roundCurrent,
             roundTotal: safeActivity.content.state.roundTotal,