Add Docker self-hosting and CI/CD pipeline

- Dockerfile: Caddy + PHP-FPM + app in single Alpine container
- Caddyfile: auto-HTTPS, security headers, short URL rewrite
- docker-compose.yml: app + Watchtower for auto-updates
- install.sh: one-liner for fresh VPS setup
- GitHub Actions: build & push to Docker Hub + GHCR on tag

Self-host with:
  curl -sL https://xmrpay.link/install.sh | sh -s your-domain.com

.dockerignore

@@ -0,0 +1,12 @@
+.git
+data/
+scripts/
+branding/
+README.md
+LICENSE
+nginx-security-headers.conf
+docker-compose.yml
+.dockerignore
+.gitignore
+app.js
+i18n.js