feat: Integrate Firebase Authentication and Firestore

- Added Firebase configuration to Android and iOS projects.
- Created `google-services.json` and `GoogleService-Info.plist` for Firebase setup.
- Implemented `AuthService` for handling user authentication with Firebase.
- Updated `UserProvider` to manage user data with Firestore.
- Refactored `ProfileContent`, `LoginPage`, and `SignUpPage` to use the new authentication service.
- Removed the old `UserService` and replaced it with Firestore-based user management.
- Added Firebase options in `firebase_options.dart` for platform-specific configurations.
- Updated dependencies in `pubspec.yaml` for Firebase packages.

ios/Runner/GoogleService-Info.plist

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CLIENT_ID</key>
+	<string>521527250907-3i1qe2656eojs8k9hjdi573j09i9p41m.apps.googleusercontent.com</string>
+	<key>REVERSED_CLIENT_ID</key>
+	<string>com.googleusercontent.apps.521527250907-3i1qe2656eojs8k9hjdi573j09i9p41m</string>
+	<key>ANDROID_CLIENT_ID</key>
+	<string>521527250907-lqgj1lmfcsjusm2be9r6kpuanq3jvjcd.apps.googleusercontent.com</string>
+	<key>API_KEY</key>
+	<string>AIzaSyBFaSzvcvO8qg7El-2jRf7WctZIMKNA4-I</string>
+	<key>GCM_SENDER_ID</key>
+	<string>521527250907</string>
+	<key>PLIST_VERSION</key>
+	<string>1</string>
+	<key>BUNDLE_ID</key>
+	<string>com.example.travelMate</string>
+	<key>PROJECT_ID</key>
+	<string>travelmate-a47f5</string>
+	<key>STORAGE_BUCKET</key>
+	<string>travelmate-a47f5.firebasestorage.app</string>
+	<key>IS_ADS_ENABLED</key>
+	<false></false>
+	<key>IS_ANALYTICS_ENABLED</key>
+	<false></false>
+	<key>IS_APPINVITE_ENABLED</key>
+	<true></true>
+	<key>IS_GCM_ENABLED</key>
+	<true></true>
+	<key>IS_SIGNIN_ENABLED</key>
+	<true></true>
+	<key>GOOGLE_APP_ID</key>
+	<string>1:521527250907:ios:64b41be39c54db1c7da1fe</string>
+</dict>
+</plist>