- Extract _cleanup() to properly unregister ADC listener + clear timers
- ADC callback unregisters itself on first receive (prevent duplicates)
- setParams failure now stops scanning and clears all state
- Timeout handler unregisters ADC listener
- Add BLE connection check before scan
- SCAN_TIMEOUT 8s → 12s (must exceed hold_time 10s)
- Pre-compute barWidth in JS instead of float math in WXML
- Error only shows when scanning is false