Remove Gorush, use direct APNs/FCM, fix worker queries

- Remove Gorush push server dependency (now using direct APNs/FCM)
- Update docker-compose.yml to remove gorush service
- Update config.go to remove GORUSH_URL
- Fix worker queries:
  - Use auth_user instead of user_user table
  - Use completed_at instead of completion_date column
- Add NotificationService to worker handler for actionable notifications
- Add docs/PUSH_NOTIFICATIONS.md with architecture documentation
- Update README.md, DOKKU_SETUP.md, and dev.sh

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

dev.sh

@@ -179,7 +179,6 @@ case "$1" in
       echo "  worker          - Background job worker"
       echo "  db              - PostgreSQL database"
       echo "  redis           - Redis cache"
-      echo "  gorush          - Push notification server"
       echo ""
       echo "Examples:"
       echo "  ./dev.sh                 # Start dev environment"