Add initial plugin implementation and development setup

dev/.env.example

@@ -0,0 +1,13 @@
+# Database URL - will use in-memory DB for development if not provided
+DATABASE_URI=mongodb://127.0.0.1/payload-notifications-dev
+
+# PayloadCMS Secret
+PAYLOAD_SECRET=your-super-secret-jwt-secret
+
+# VAPID Keys for Web Push Notifications
+# Generate with: npx web-push generate-vapid-keys
+VAPID_PUBLIC_KEY=BMrF5MbHcaEo6w4lPjG9m3BvONvFPfz7jLJ9t0F9yJGzSI3ZUHQj9fNUP7w2D8h1kI4x3YzJ1a4f0nS5g6t2F9L
+VAPID_PRIVATE_KEY=your-vapid-private-key-here
+
+# Development Settings
+NODE_ENV=development