feat: scaffold Expo Prebuild project with all v1 screens and services

Sets up the full bincio-rec source tree: Zustand recording store with
haversine stats, background GPS via expo-task-manager, BLE scan/subscribe
for HR and power, GPX writer with Garmin extensions, SQLite recordings
list, multipart upload to bincio-activity, React Navigation stack with
bottom tabs, and build instructions in README.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

App.tsx

@@ -1,20 +1,12 @@
 import { StatusBar } from 'expo-status-bar';
-import { StyleSheet, Text, View } from 'react-native';
+import { GestureHandlerRootView } from 'react-native-gesture-handler';
+import { AppNavigator } from './src/navigation/AppNavigator';
 
 export default function App() {
   return (
-    <View style={styles.container}>
-      <Text>Open up App.tsx to start working on your app!</Text>
-      <StatusBar style="auto" />
-    </View>
+    <GestureHandlerRootView style={{ flex: 1 }}>
+      <StatusBar style="light" />
+      <AppNavigator />
+    </GestureHandlerRootView>
   );
 }
-
-const styles = StyleSheet.create({
-  container: {
-    flex: 1,
-    backgroundColor: '#fff',
-    alignItems: 'center',
-    justifyContent: 'center',
-  },
-});