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/_layout.tsx

@@ -0,0 +1,81 @@
+/**
+ * Root layout for the DocuElevate mobile app.
+ *
+ * Wraps the entire app in AuthProvider and SafeAreaProvider, then uses the
+ * AuthGuard component to redirect between the unauthenticated (auth) route
+ * group and the authenticated (tabs) route group based on session state.
+ */
+
+import { Stack, useRouter, useSegments } from "expo-router";
+import React, { useEffect } from "react";
+import { ActivityIndicator, StyleSheet, Text, View } from "react-native";
+import { SafeAreaProvider } from "react-native-safe-area-context";
+import { AuthProvider, useAuth } from "../src/context/AuthContext";
+
+// ---------------------------------------------------------------------------
+// Auth guard – redirects to the correct route group after auth state resolves
+// ---------------------------------------------------------------------------
+
+function AuthGuard() {
+  const { isLoading, isAuthenticated } = useAuth();
+  const segments = useSegments();
+  const router = useRouter();
+
+  useEffect(() => {
+    if (isLoading) return;
+
+    const inAuthGroup = segments[0] === "(auth)";
+
+    if (!isAuthenticated && !inAuthGroup) {
+      // Unauthenticated visitor outside the auth group → send to welcome
+      router.replace("/(auth)/");
+    } else if (isAuthenticated && inAuthGroup) {
+      // Authenticated user on auth screens → send to main app
+      router.replace("/(tabs)/");
+    }
+  }, [isAuthenticated, isLoading, segments, router]);
+
+  if (isLoading) {
+    return (
+      <View style={styles.loading}>
+        <ActivityIndicator size="large" color="#1e40af" />
+        <Text style={styles.loadingText}>Loading…</Text>
+      </View>
+    );
+  }
+
+  return (
+    <Stack screenOptions={{ headerShown: false }}>
+      <Stack.Screen name="(auth)" />
+      <Stack.Screen name="(tabs)" />
+    </Stack>
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Root layout export
+// ---------------------------------------------------------------------------
+
+export default function RootLayout() {
+  return (
+    <SafeAreaProvider>
+      <AuthProvider>
+        <AuthGuard />
+      </AuthProvider>
+    </SafeAreaProvider>
+  );
+}
+
+const styles = StyleSheet.create({
+  loading: {
+    flex: 1,
+    alignItems: "center",
+    justifyContent: "center",
+    backgroundColor: "#f9fafb",
+    gap: 12,
+  },
+  loadingText: {
+    color: "#6b7280",
+    fontSize: 15,
+  },
+});