feat: setup navigation structure with Expo Router

frontend-mobile/app/(tabs)/map.tsx

@@ -0,0 +1,23 @@
+import { View, Text, StyleSheet } from 'react-native';
+
+export default function MapScreen() {
+  return (
+    <View style={styles.container}>
+      <Text style={styles.title}>Mapa de Farmacias</Text>
+    </View>
+  );
+}
+
+const styles = StyleSheet.create({
+  container: {
+    flex: 1,
+    justifyContent: 'center',
+    alignItems: 'center',
+    backgroundColor: '#F2F2F7',
+  },
+  title: {
+    fontSize: 24,
+    fontWeight: 'bold',
+    color: '#1C1C1E',
+  },
+});