feat: section 2 — BLE permissions, cadence parsing, sensor persistence

- requestBlePermissions() handles BLUETOOTH_SCAN + BLUETOOTH_CONNECT on Android 12+
- parseCscMeasurement() implements stateful CSC crank RPM with uint16 rollover
- savePairedDevice / loadPairedDevices / removePairedDevice via AsyncStorage
- SensorPairingScreen: saved sensors section, auto-reconnect on mount, Forget button

CLAUDE.md

@@ -106,11 +106,11 @@ Items below are what remains before v1 is shippable.
 - [x] **GPS pause/resume** — `handlePause` calls `stopGpsRecording()`, `handleResume` calls `startGpsRecording()`
 - [x] **Track view** — `TrackView` component renders recorded lat/lon points as a scaled SVG polyline on a dark background (no tile server needed); replaces the grey placeholder
 
-### 2 — BLE (half day)
+### 2 — BLE ✅
 
-- [ ] **Android runtime permissions** — `BLUETOOTH_SCAN` + `BLUETOOTH_CONNECT` require explicit permission requests on Android 12+; add a `requestBlePermissions()` call in `SensorPairingScreen` before scanning
-- [ ] **Cadence CSC parsing** — `subscribeCadence()` in `ble.ts` is stubbed; implement stateful CSC Measurement parsing (track previous crank revolution count + timestamp, compute RPM from delta)
-- [ ] **BLE persistence** — save paired device IDs + types to AsyncStorage on connect; on app start, attempt to reconnect to previously paired devices automatically
+- [x] **Android runtime permissions** — `requestBlePermissions()` requests `BLUETOOTH_SCAN` + `BLUETOOTH_CONNECT` on Android 12+ (API 31+) before scanning
+- [x] **Cadence CSC parsing** — stateful parsing in `parseCscMeasurement()`: tracks previous crank revolution count + event time (uint16, 1/1024 s), computes RPM from delta with uint16 rollover handling
+- [x] **BLE persistence** — `savePairedDevice` / `loadPairedDevices` / `removePairedDevice` in `ble.ts` via AsyncStorage; SensorPairingScreen shows saved sensors at top, auto-attempts reconnect on mount, Forget button removes a device
 
 ### 3 — Km notifications (half day)