feat: Sprint 5 — PIN lock, biometric auth, sync screen, QR code, merge logic

- lib/pinService.ts: PIN storage/verification via expo-secure-store
- lib/syncService.ts: sync abstraction with full merge logic (mDNS/TCP stubbed)
- app/lock.tsx: full-screen PIN lock with biometric support
- components/ui/PinPad.tsx: reusable 6-digit PIN pad component
- components/sync/QRScanner.tsx: QR code scanner via expo-camera
- app/(tabs)/sync.tsx: Sync tab with QR display, partner input, history
- app/sync-progress.tsx: animated sync progress screen with summary
- app/(tabs)/settings.tsx: full settings with PIN setup, security, data sections
- app/(tabs)/_layout.tsx: added Sync tab (RefreshCw icon)
- app/_layout.tsx: AppState listener locks app after 60s background
- package.json: added expo-secure-store, react-native-qrcode-svg

lib/pinService.ts

@@ -0,0 +1,52 @@
+// lib/pinService.ts
+import * as SecureStore from 'expo-secure-store';
+
+const PIN_KEY = 'territory_log_pin';
+const PIN_ENABLED_KEY = 'territory_log_pin_enabled';
+const BIOMETRIC_ENABLED_KEY = 'territory_log_biometric_enabled';
+
+export async function isPinEnabled(): Promise<boolean> {
+  try {
+    const val = await SecureStore.getItemAsync(PIN_ENABLED_KEY);
+    return val === 'true';
+  } catch {
+    return false;
+  }
+}
+
+export async function setPin(pin: string): Promise<void> {
+  await SecureStore.setItemAsync(PIN_KEY, pin);
+  await SecureStore.setItemAsync(PIN_ENABLED_KEY, 'true');
+}
+
+export async function verifyPin(pin: string): Promise<boolean> {
+  try {
+    const stored = await SecureStore.getItemAsync(PIN_KEY);
+    return stored === pin;
+  } catch {
+    return false;
+  }
+}
+
+export async function disablePin(): Promise<void> {
+  await SecureStore.deleteItemAsync(PIN_KEY);
+  await SecureStore.setItemAsync(PIN_ENABLED_KEY, 'false');
+  await SecureStore.setItemAsync(BIOMETRIC_ENABLED_KEY, 'false');
+}
+
+export async function getPinEnabled(): Promise<boolean> {
+  return isPinEnabled();
+}
+
+export async function isBiometricEnabled(): Promise<boolean> {
+  try {
+    const val = await SecureStore.getItemAsync(BIOMETRIC_ENABLED_KEY);
+    return val === 'true';
+  } catch {
+    return false;
+  }
+}
+
+export async function setBiometricEnabled(enabled: boolean): Promise<void> {
+  await SecureStore.setItemAsync(BIOMETRIC_ENABLED_KEY, enabled ? 'true' : 'false');
+}