feat: Implement push notifications in Budget Manager PWA

- Added functionality for subscribing to push notifications in Settings.vue.
- Integrated service worker registration and notification permission requests.
- Enhanced Vite configuration for PWA with manifest and caching strategies.
- Created a script for generating PDF reports.
- Added project report markdown file detailing the PWA implementation and features.

backend/.env.example

@@ -0,0 +1,14 @@
+# JWT Secret for authentication
+JWT_SECRET=your_jwt_secret_here
+
+# MongoDB connection
+MONGODB_URI=mongodb://localhost:27017/budget_manager
+
+# VAPID Keys for Web Push Notifications
+# Generate your own keys using the script in /scripts/generate-vapid-keys.js
+VAPID_PUBLIC_KEY=BEHsROsRzfqdMv4g50BEKUbFEL0NNdig0yxdmd-d9j5ZNLOOWbwsTZY3q_W_Y2E-h-hCCJmC5r3uATdFKQTN4z0
+VAPID_PRIVATE_KEY=dhty4Wi3rKZlKRs_7zSPmcW6qEK8sCMZ23Qw9iMGuBM
+
+# App settings
+PORT=3000
+NODE_ENV=development