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

Dockerfile

@@ -0,0 +1,38 @@
+FROM php:8.3-fpm-alpine AS base
+
+# Install PHP curl extension (needed for API proxies)
+RUN apk add --no-cache caddy curl-dev \
+    && docker-php-ext-install curl \
+    && rm -rf /var/cache/apk/*
+
+# PHP-FPM tuning for low-memory VPS
+RUN { \
+      echo '[www]'; \
+      echo 'pm = ondemand'; \
+      echo 'pm.max_children = 8'; \
+      echo 'pm.process_idle_timeout = 60s'; \
+    } > /usr/local/etc/php-fpm.d/zz-tuning.conf
+
+# App files
+COPY index.html privacy.html style.css sw.js favicon.svg s.php /srv/
+COPY app.min.js /srv/app.min.js
+COPY i18n.min.js /srv/i18n.min.js
+COPY api/ /srv/api/
+COPY lib/ /srv/lib/
+COPY fonts/ /srv/fonts/
+
+# Writable data directory
+RUN mkdir -p /srv/data && chown www-data:www-data /srv/data
+
+# Caddyfile
+COPY Caddyfile /etc/caddy/Caddyfile
+
+# Entrypoint: start PHP-FPM + Caddy
+COPY docker-entrypoint.sh /usr/local/bin/
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+
+EXPOSE 80 443
+
+VOLUME ["/srv/data", "/data/caddy"]
+
+ENTRYPOINT ["docker-entrypoint.sh"]