Initialize Expo mobile app with tab navigation and monorepo support

- Expo managed project at apps/mobile/ with TypeScript
- Expo Router with 4 tabs: Map, Routes, Activities, Profile
- app.config.ts with monorepo experiment, bundle IDs, scheme
- Workspace packages linked: api, gpx, i18n, map-core, types
- Profile tab imports API_VERSION from @trails-cool/api to verify
  shared package resolution

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/mobile/app.config.ts

@@ -0,0 +1,36 @@
+import { ExpoConfig, ConfigContext } from "expo/config";
+
+export default ({ config }: ConfigContext): ExpoConfig => ({
+  ...config,
+  name: "trails.cool",
+  slug: "trails-cool",
+  version: "0.0.1",
+  scheme: "trailscool",
+  orientation: "portrait",
+  icon: "./assets/icon.png",
+  userInterfaceStyle: "light",
+  newArchEnabled: true,
+  splash: {
+    image: "./assets/splash-icon.png",
+    resizeMode: "contain",
+    backgroundColor: "#ffffff",
+  },
+  ios: {
+    supportsTablet: true,
+    bundleIdentifier: "cool.trails.app",
+  },
+  android: {
+    adaptiveIcon: {
+      foregroundImage: "./assets/adaptive-icon.png",
+      backgroundColor: "#ffffff",
+    },
+    package: "cool.trails.app",
+  },
+  web: {
+    favicon: "./assets/favicon.png",
+  },
+  experiments: {
+    monorepo: true,
+  },
+  plugins: ["expo-router"],
+});