docs: add nginx-proxy + acme companion guide

docs/03-production/04-nginx-proxy-acme-companion.md

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+# nginx-proxy + acme-companion (HTTPS)
+
+This guide explains how to use nginx-proxy with acme-companion to provide HTTPS for a Frappe Docker stack.
+
+## When to choose this
+
+- You want a simple, host-based reverse proxy
+- You run a single bench or only a few hostnames
+- You prefer environment-variable based configuration
+
+If you need advanced routing or complex multi-site setups, **Traefik** is usually the better choice.
+
+## Prerequisites
+
+- Public DNS points your domain(s) to the server
+- Ports 80 and 443 are reachable (HTTP-01 challenge)
+- Docker and Docker Compose v2 installed
+
+## Required environment variables
+
+Set these in `.env`:
+
+```bash
+NGINX_PROXY_HOSTS=erp.your-domain.com
+LETSENCRYPT_EMAIL=admin@your-domain.com
+```
+
+Multiple hostnames (comma-separated, no spaces):
+
+```bash
+NGINX_PROXY_HOSTS=erp.your-domain.com,erp2.your-domain.com
+LETSENCRYPT_EMAIL=admin@example.com
+```
+
+Optional (non-default ports):
+
+```bash
+HTTP_PUBLISH_PORT=80
+HTTPS_PUBLISH_PORT=443
+```
+
+## Compose setup (HTTPS)
+
+For HTTPS you must include both overrides:
+
+- `overrides/compose.nginxproxy.yaml` (nginx-proxy, VIRTUAL_HOST)
+- `overrides/compose.nginxproxy-ssl.yaml` (acme-companion, LETSENCRYPT_HOST)
+
+Example:
+
+```sh
+docker compose -f compose.yaml \
+  -f overrides/compose.mariadb.yaml \
+  -f overrides/compose.redis.yaml \
+  -f overrides/compose.nginxproxy.yaml \
+  -f overrides/compose.nginxproxy-ssl.yaml \
+  config > ~/gitops/docker-compose.yml
+
+docker compose --project-name <project-name> -f ~/gitops/docker-compose.yml up -d
+```
+
+> If you use external MariaDB/Redis, replace the database and Redis overrides accordingly.
+
+## How hostnames are applied
+
+`NGINX_PROXY_HOSTS` is a comma-separated list of hostnames. The overrides apply it as:
+
+- `VIRTUAL_HOST` for nginx-proxy routing
+- `LETSENCRYPT_HOST` for certificate issuance
+
+## Verify
+
+Check logs for certificate issuance and proxy status:
+
+```sh
+docker compose --project-name <project-name> -f ~/gitops/docker-compose.yml logs -f nginx-proxy
+docker compose --project-name <project-name> -f ~/gitops/docker-compose.yml logs -f acme-companion
+```
+
+> Depending on the registrar, the assignment may take some time, whereby it must also be ensured that A and AAAA records are correctly directed to the server for the issuance of the certificate, if necessary.
+
+See also: [Environment Variables](../02-setup/04-env-variables.md) and [TLS/SSL Setup Overview](01-tls-ssl-setup.md).