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.

DOCKER_PUSH_NOTIFICATIONS_SETUP.md

@@ -0,0 +1,115 @@
+# Push Notifications Setup for Docker
+
+## Quick Setup (3 Steps)
+
+### Step 1: Generate VAPID Keys
+
+Run this **on your host machine** (not in Docker):
+
+```bash
+npx web-push generate-vapid-keys
+```
+
+Or if you prefer, you can run it in a temporary container:
+
+```bash
+docker run --rm -it node:20-slim sh -c "npm install -g web-push && web-push generate-vapid-keys"
+```
+
+This will output:
+```
+=======================================
+Public Key:
+BNxxx...
+
+Private Key:
+xxx...
+=======================================
+```
+
+### Step 2: Add Keys to .env File
+
+Add these three lines to your `.env` file:
+
+```env
+VAPID_PUBLIC_KEY=BNxxx...
+VAPID_PRIVATE_KEY=xxx...
+VAPID_SUBJECT=mailto:your-email@example.com
+```
+
+⚠️ **Important**: 
+- Replace `BNxxx...` with your actual public key
+- Replace `xxx...` with your actual private key
+- Replace `your-email@example.com` with your actual email
+- Keep the VAPID_PRIVATE_KEY secret!
+
+### Step 3: Update Database Schema
+
+Run this to add the PushSubscription table:
+
+```bash
+docker-compose exec app npx prisma db push
+```
+
+Or if your containers aren't running yet:
+
+```bash
+docker-compose up -d
+docker-compose exec app npx prisma db push
+```
+
+### Step 4: Rebuild and Restart
+
+```bash
+docker-compose down
+docker-compose up --build
+```
+
+## That's It!
+
+Your app now has push notifications enabled! When users open the app:
+- After 3 seconds, they'll see a notification prompt
+- They can enable notifications with one click
+- Notifications will be sent automatically for list events
+
+## Verify It's Working
+
+1. Open your app at `http://localhost:3500`
+2. Log in
+3. Wait 3 seconds for the notification prompt
+4. Click "Enable Notifications"
+5. Open another browser/incognito window
+6. Log in as a different user
+7. Add an item to a shared list
+8. See the notification in the first browser!
+
+## Troubleshooting
+
+### "Push notifications not configured" error
+- Make sure VAPID keys are in `.env`
+- Make sure you rebuilt the containers: `docker-compose up --build`
+- Check logs: `docker-compose logs app`
+
+### Database table missing
+- Run: `docker-compose exec app npx prisma db push`
+- Check if it succeeded: `docker-compose exec app npx prisma studio`
+
+### Environment variables not loading
+- Make sure `.env` is in the same directory as `docker-compose.yml`
+- Restart containers: `docker-compose restart`
+- Check if variables are loaded: `docker-compose exec app env | grep VAPID`
+
+## Docker-Specific Notes
+
+- The `web-push` package is automatically installed during `docker-compose up --build`
+- VAPID keys are loaded from your `.env` file into the container
+- The database schema update must be run inside the container
+- All notification functionality works the same in Docker as locally
+
+## Production Deployment
+
+For production:
+1. Generate production VAPID keys (different from dev)
+2. Add them to your production environment variables
+3. Run `npx prisma db push` in production container
+4. Ensure your production URL uses HTTPS (required for push notifications)