feat(ecg): compute heart rate from R-peaks and improve WFDB validation
- Replace annotation-based RR calculation with ComputeHeartRate()
- Track recent R-peaks and calculate BPM from RR interval
- Reject duplicate and invalid RR intervals
- Update ProcessSingleLead to use latest R-peak index
- Improve P-wave start detection sensitivity
- Add sel103 heart rate validation test
- Add CSV output for reference and detected BPM/QRS
- Apply baseline removal for WFDB ECG processing
- Clean up debug code and refactor tests