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/Utilities/Strings.swift

@@ -175,7 +175,11 @@ enum L10n {
         static let pill4MinWorkouts       = LocalizedStringResource("onboarding.pill4MinWorkouts")
         static let pillNoEquipment        = LocalizedStringResource("onboarding.pillNoEquipment")
         static let pillVoiceGuided        = LocalizedStringResource("onboarding.pillVoiceGuided")
-        static let tabataDesc             = LocalizedStringResource("onboarding.tabataDesc")
+        static let healthAccess            = LocalizedStringResource("onboarding.healthAccess")
+        static let healthAccessSubtitle    = LocalizedStringResource("onboarding.healthAccessSubtitle")
+        static let allowHealthAccess       = LocalizedStringResource("onboarding.allowHealthAccess")
+        static let notNow                  = LocalizedStringResource("onboarding.notNow")
+        static let tabataDesc              = LocalizedStringResource("onboarding.tabataDesc")
 
         enum levelDesc {
             static let beginner     = LocalizedStringResource("onboarding.level.beginnerDesc")