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

app/lock.tsx

@@ -0,0 +1,205 @@
+// app/lock.tsx — Full-screen PIN lock screen
+import React, { useEffect, useState, useCallback } from 'react';
+import {
+  View,
+  Text,
+  StyleSheet,
+  Alert,
+  TouchableOpacity,
+  SafeAreaView,
+} from 'react-native';
+import { router } from 'expo-router';
+import * as LocalAuthentication from 'expo-local-authentication';
+import { Shield } from 'lucide-react-native';
+import PinPad from '@/components/ui/PinPad';
+import { verifyPin, disablePin } from '@/lib/pinService';
+import { getDatabase } from '@/lib/database';
+import { useUserStore } from '@/store/useUserStore';
+
+export default function LockScreen() {
+  const [pin, setPin] = useState('');
+  const [error, setError] = useState('');
+  const [biometricAvailable, setBiometricAvailable] = useState(false);
+  const clearUser = useUserStore((s) => s.clearUser);
+
+  useEffect(() => {
+    checkBiometric();
+  }, []);
+
+  const checkBiometric = async () => {
+    try {
+      const hardware = await LocalAuthentication.hasHardwareAsync();
+      const enrolled = await LocalAuthentication.isEnrolledAsync();
+      setBiometricAvailable(hardware && enrolled);
+    } catch {
+      setBiometricAvailable(false);
+    }
+  };
+
+  const handleBiometric = useCallback(async () => {
+    try {
+      const result = await LocalAuthentication.authenticateAsync({
+        promptMessage: 'Unlock TerritoryLog',
+        fallbackLabel: 'Use PIN',
+        cancelLabel: 'Cancel',
+      });
+      if (result.success) {
+        router.replace('/(tabs)');
+      } else {
+        setError('Biometric authentication failed. Use your PIN.');
+      }
+    } catch {
+      setError('Biometric not available.');
+    }
+  }, []);
+
+  // Auto-trigger biometric on mount if available
+  useEffect(() => {
+    if (biometricAvailable) {
+      handleBiometric();
+    }
+  }, [biometricAvailable, handleBiometric]);
+
+  const handlePinChange = async (newPin: string) => {
+    setPin(newPin);
+    setError('');
+
+    if (newPin.length === 6) {
+      const ok = await verifyPin(newPin);
+      if (ok) {
+        router.replace('/(tabs)');
+      } else {
+        setError('Incorrect PIN. Try again.');
+        setTimeout(() => setPin(''), 600);
+      }
+    }
+  };
+
+  const handleForgotPin = () => {
+    Alert.alert(
+      'Forgot PIN?',
+      'Resetting your PIN will clear ALL app data. This cannot be undone.',
+      [
+        { text: 'Cancel', style: 'cancel' },
+        {
+          text: 'Clear & Reset',
+          style: 'destructive',
+          onPress: async () => {
+            try {
+              const db = await getDatabase();
+              await db.execAsync(`
+                DELETE FROM contacts;
+                DELETE FROM visits;
+                DELETE FROM territories;
+                DELETE FROM users;
+                DELETE FROM sync_log;
+                DELETE FROM topics;
+              `);
+              await disablePin();
+              clearUser();
+              router.replace('/onboarding');
+            } catch (e) {
+              Alert.alert('Error', 'Could not clear data. Please try again.');
+            }
+          },
+        },
+      ]
+    );
+  };
+
+  return (
+    <SafeAreaView style={styles.container}>
+      <View style={styles.content}>
+        {/* Logo */}
+        <View style={styles.logoArea}>
+          <View style={styles.iconCircle}>
+            <Shield size={40} color="#1A6B72" />
+          </View>
+          <Text style={styles.appName}>TerritoryLog</Text>
+          <Text style={styles.subtitle}>Enter your PIN to continue</Text>
+        </View>
+
+        {/* Error */}
+        {error ? <Text style={styles.error}>{error}</Text> : null}
+
+        {/* PIN Pad */}
+        <PinPad pin={pin} onPinChange={handlePinChange} maxLength={6} />
+
+        {/* Biometric button */}
+        {biometricAvailable && (
+          <TouchableOpacity style={styles.biometricBtn} onPress={handleBiometric}>
+            <Text style={styles.biometricText}>Use Biometrics</Text>
+          </TouchableOpacity>
+        )}
+
+        {/* Forgot PIN */}
+        <TouchableOpacity style={styles.forgotBtn} onPress={handleForgotPin}>
+          <Text style={styles.forgotText}>Forgot PIN? (Clear App Data)</Text>
+        </TouchableOpacity>
+      </View>
+    </SafeAreaView>
+  );
+}
+
+const styles = StyleSheet.create({
+  container: {
+    flex: 1,
+    backgroundColor: '#111827',
+  },
+  content: {
+    flex: 1,
+    alignItems: 'center',
+    justifyContent: 'center',
+    paddingHorizontal: 24,
+    gap: 32,
+  },
+  logoArea: {
+    alignItems: 'center',
+    gap: 12,
+  },
+  iconCircle: {
+    width: 80,
+    height: 80,
+    borderRadius: 40,
+    backgroundColor: 'rgba(26,107,114,0.15)',
+    justifyContent: 'center',
+    alignItems: 'center',
+    borderWidth: 2,
+    borderColor: 'rgba(26,107,114,0.4)',
+  },
+  appName: {
+    fontSize: 28,
+    fontWeight: '700',
+    color: '#F9FAFB',
+    letterSpacing: 0.5,
+  },
+  subtitle: {
+    fontSize: 15,
+    color: '#9CA3AF',
+  },
+  error: {
+    color: '#F87171',
+    fontSize: 14,
+    textAlign: 'center',
+  },
+  biometricBtn: {
+    paddingVertical: 12,
+    paddingHorizontal: 28,
+    borderRadius: 24,
+    borderWidth: 1,
+    borderColor: '#1A6B72',
+  },
+  biometricText: {
+    color: '#1A6B72',
+    fontSize: 15,
+    fontWeight: '600',
+  },
+  forgotBtn: {
+    marginTop: 8,
+  },
+  forgotText: {
+    color: '#6B7280',
+    fontSize: 13,
+    textDecorationLine: 'underline',
+  },
+});