feat: move HealthKit permission to onboarding, remove HR write

- Add .health step to onboarding between frequency and ready
- HealthStep with non-blocking permission flow (Not Now skips)
- Remove requestAuthorization() from PlayerViewModel.startWorkout()
- Guard live session start with isAuthorized check
- Remove heart rate write from HealthKit authorization popup
- Remove HR sample writing from saveWorkout (now without permission)
- Add L10n keys: healthAccess, healthAccessSubtitle, allowHealthAccess, notNow
- Add EN/DE/ES/FR translations
- Track permission decisions through analytics
- Entry animation on HealthStep (fade-in + slide-up)

HealthKit permission is now asked once during onboarding,
never interrupting workouts again.

tabatago-swift/TabataGo/Views/Onboarding/OnboardingView.swift

@@ -12,7 +12,7 @@ struct OnboardingView: View {
     @Environment(\.modelContext) private var context
 
     enum Step: Int, CaseIterable {
-        case welcome, name, level, goal, frequency, ready
+        case welcome, name, level, goal, frequency, health, ready
         var progress: Double { Double(rawValue) / Double(Step.allCases.count - 1) }
     }
 
@@ -67,6 +67,7 @@ struct OnboardingView: View {
                     case .level:     LevelStep(selection: $fitnessLevel)
                     case .goal:      GoalStep(selection: $goal)
                     case .frequency: FrequencyStep(frequency: $weeklyFrequency, barriers: $selectedBarriers, allBarriers: barriers)
+                    case .health:    HealthStep(onContinue: { advance() })
                     case .ready:     ReadyStep(name: name)
                     }
                 }
@@ -77,11 +78,13 @@ struct OnboardingView: View {
                 .animation(.spring(duration: 0.45), value: step)
 
                 // ── Pinned bottom button ─────────────────────────
-                PrimaryButton(label: buttonLabel, action: buttonAction)
-                    .disabled(step == .name && name.trimmingCharacters(in: .whitespaces).isEmpty)
-                    .padding(.horizontal, 32)
-                    .padding(.bottom, 48)
-                    .padding(.top, 16)
+                if step != .health {
+                    PrimaryButton(label: buttonLabel, action: buttonAction)
+                        .disabled(step == .name && name.trimmingCharacters(in: .whitespaces).isEmpty)
+                        .padding(.horizontal, 32)
+                        .padding(.bottom, 48)
+                        .padding(.top, 16)
+                }
             }
         }
     }
@@ -411,6 +414,68 @@ private struct FrequencyStep: View {
     }
 }
 
+private struct HealthStep: View {
+    let onContinue: () -> Void
+    @State private var isRequesting = false
+    @State private var appeared = false
+
+    var body: some View {
+        VStack(spacing: 36) {
+            Spacer()
+
+            Image(systemName: "heart.text.square")
+                .font(.system(size: 80))
+                .foregroundStyle(Theme.brand.gradient)
+
+            OnboardingHeader(title: L10n.onboarding.healthAccess, subtitle: L10n.onboarding.healthAccessSubtitle)
+
+            // Primary button — reuses shared PrimaryButton component
+            PrimaryButton(label: L10n.onboarding.allowHealthAccess, action: requestHealthAccess)
+                .disabled(isRequesting)
+                .padding(.horizontal, 32)
+
+            // Skip option
+            Button {
+                onContinue()
+            } label: {
+                Text(L10n.onboarding.notNow)
+                    .font(.subheadline.weight(.medium))
+                    .foregroundStyle(.secondary)
+            }
+            .buttonStyle(.plain)
+            .disabled(isRequesting)
+
+            Spacer()
+        }
+        .opacity(appeared ? 1 : 0)
+        .offset(y: appeared ? 0 : 14)
+        .onAppear {
+            withAnimation(.spring(duration: 0.45)) { appeared = true }
+        }
+    }
+
+    private func requestHealthAccess() {
+        guard !isRequesting else { return }
+        isRequesting = true
+        Task {
+            do {
+                try await HealthKitService.shared.requestAuthorization()
+            } catch {
+                print("[HealthStep] HealthKit authorization error: \(error)")
+                // Continue — user can try later in Settings
+            }
+            let authorized = await HealthKitService.shared.isAuthorized
+            if authorized {
+                AnalyticsService.shared.healthKitPermissionGranted()
+            } else {
+                AnalyticsService.shared.healthKitPermissionDenied()
+            }
+            isRequesting = false
+            onContinue()
+        }
+    }
+}
+
 private struct ReadyStep: View {
     let name: String
     @State private var showContent = false