fix(mobile): correct asset logo path depth and add expo-router app/ routes for web support

- Fix fatal crash: require('../../../assets/logo.png') in LoginScreen and
  WelcomeScreen resolved 3 levels above mobile/src/screens/ — outside the
  mobile/ directory. Changed to ../../assets/logo.png which correctly
  resolves to the existing mobile/assets/logo.png.
- Add expo-router app/ directory (root cause of missing welcome screen and
  web support): app/_layout.tsx, (auth)/, (tabs)/ with all route files
- Add WelcomeScreen.tsx: branded intro screen with feature highlights
- Update LoginScreen/WelcomeScreen to use useRouter() (expo-router style)
- Add react-native-web ~0.20.0 and react-dom 19.2.4 for web channel
- Add expo-device ~7.0.3 (was imported but missing from package.json)
- Remove android.googleServicesFile from app.json (file is gitignored;
  README documents how to restore it for Android FCM builds)
- Add web.bundler: metro and web.output: single to app.json
- Fix aria-hidden to explicit boolean value in WelcomeScreen

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

mobile/app/(auth)/_layout.tsx

@@ -0,0 +1,17 @@
+/**
+ * Layout for the unauthenticated route group: Welcome → Login.
+ *
+ * Uses a headerless native stack so the screens animate naturally.
+ */
+
+import { Stack } from "expo-router";
+import React from "react";
+
+export default function AuthLayout() {
+  return (
+    <Stack screenOptions={{ headerShown: false }}>
+      <Stack.Screen name="index" />
+      <Stack.Screen name="login" />
+    </Stack>
+  );
+}

mobile/app/(auth)/index.tsx

@@ -0,0 +1,4 @@
+/**
+ * Welcome screen route – first screen shown to unauthenticated users.
+ */
+export { default } from "../../src/screens/WelcomeScreen";

mobile/app/(auth)/login.tsx

@@ -0,0 +1,4 @@
+/**
+ * Login screen route – server URL entry and SSO sign-in.
+ */
+export { default } from "../../src/screens/LoginScreen";