Add Strava upload, workout activity copying, and platform limitations docs
- Add StravaManager with OAuth login, TCX generation, and upload via
Strava API (client ID/secret are placeholders)
- Add Strava connect/upload/disconnect UI to workout edit view
- Copy HKWorkoutActivity objects during trim so Apple Fitness can
display splits
- Expand authorization and migrated sample types (running dynamics,
effort scores, basal energy, step count, VO2 max)
- Fetch effort scores by time range and relate via special iOS 18 API
- Document all HealthKit and Strava platform limitations in README