feat: add auto-prompt for push notifications on app load

- Create NotificationPrompt component that appears 3 seconds after app loads
- Add to main layout so it shows on all pages (for logged-in users)
- Prompt only shows if permission not yet requested
- Users can dismiss temporarily or permanently
- Add slide-up animation for smooth appearance
- Create simplified SETUP_PUSH_NOTIFICATIONS.md guide

Users will now be automatically prompted to enable notifications
instead of having to go to the profile page.

SETUP_PUSH_NOTIFICATIONS.md

@@ -0,0 +1,83 @@
+# Setup Push Notifications - Required Steps
+
+## You MUST do these 3 steps for notifications to work:
+
+### Step 1: Install the web-push package
+```bash
+npm install
+```
+
+This installs the `web-push` package that was added to package.json.
+
+### Step 2: Generate VAPID keys
+```bash
+npm run vapid:generate
+```
+
+This will output something like:
+```
+VAPID_PUBLIC_KEY=BNxxx...
+VAPID_PRIVATE_KEY=xxx...
+VAPID_SUBJECT=mailto:your-email@example.com
+```
+
+**Copy these 3 lines and add them to your `.env` file.**
+
+⚠️ **Important**: Keep the VAPID_PRIVATE_KEY secret! Don't commit it to git.
+
+### Step 3: Update your database
+```bash
+npx prisma db push
+```
+
+This adds the `PushSubscription` table to your database.
+
+### Step 4: Restart your server
+```bash
+npm run dev
+```
+
+## That's it!
+
+Now when users open your app:
+- After 3 seconds, they'll see a notification prompt at the bottom-right
+- They can click "Enable Notifications" to subscribe
+- Or they can dismiss it and enable later from their profile page
+
+## What happens automatically:
+
+✅ Notification prompt appears 3 seconds after app loads
+✅ Only shows if user hasn't been asked before
+✅ Users can dismiss temporarily ("Later") or permanently ("Don't ask again")
+✅ Notifications are sent when:
+  - Items are added/removed/completed in shared lists
+  - Users are invited to lists
+  - Invitations are accepted
+  - Collaborators are removed
+
+## Testing
+
+1. Open your app in Chrome
+2. Wait 3 seconds
+3. Click "Enable Notifications" when the prompt appears
+4. Open another browser/incognito window
+5. Log in as a different user
+6. Add an item to a shared list
+7. See the notification in the first browser!
+
+## Troubleshooting
+
+**"Push notifications not configured" error**
+- Make sure you ran `npm run vapid:generate`
+- Make sure you added the keys to `.env`
+- Restart your dev server
+
+**Prompt doesn't appear**
+- Check browser console for errors
+- Make sure you're on localhost or HTTPS
+- Clear localStorage and refresh if you dismissed it permanently
+
+**Notifications don't send**
+- Check server console for errors
+- Verify VAPID keys are correct in `.env`
+- Make sure database was updated with `npx prisma db push`