feat: add Docker support for push notifications

- Update docker-compose.yml to include VAPID environment variables
- Create DOCKER_PUSH_NOTIFICATIONS_SETUP.md with Docker-specific instructions
- Create PUSH_NOTIFICATIONS_DOCKER_CHECKLIST.md for easy setup tracking
- Update .env.example with Docker command for generating VAPID keys

Setup for Docker:
1. Generate VAPID keys (npx web-push generate-vapid-keys)
2. Add keys to .env file
3. Run: docker-compose exec app npx prisma db push
4. Rebuild: docker-compose up --build

The web-push package is automatically installed during docker build.
All notification functionality works the same in Docker as locally.

.env.example

@@ -9,7 +9,8 @@ NEXTAUTH_SECRET=your-secret-key-here-please-change-in-production
 AUTH_SECRET=your-secret-key-here-please-change-in-production
 
 # Web Push Notifications (VAPID)
-# Generate keys with: npm run vapid:generate
+# Generate keys with: npx web-push generate-vapid-keys
+# Or in Docker: docker run --rm -it node:20-slim sh -c "npm install -g web-push && web-push generate-vapid-keys"
 VAPID_PUBLIC_KEY=your-vapid-public-key-here
 VAPID_PRIVATE_KEY=your-vapid-private-key-here
 VAPID_SUBJECT=mailto:your-email@example.com