Add Euro Office documentation and HTTP/3 (QUIC) Nginx configuration

docs/admin/configuration/euro-office/_category_.json

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+{
+  "label": "Euro Office",
+  "position": 31
+}

docs/admin/configuration/euro-office/index.md

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+---
+sidebar_position: 1
+id: euro-office
+title: Euro Office
+description: Configuration guides for Euro Office integration in OpenCloud
+draft: false
+---
+
+# Euro Office
+
+[Euro Office](https://github.com/EURO-office/DocumentServer) is a sovereign document editing suite based on ONLYOFFICE that integrates with OpenCloud via the WOPI protocol.
+
+:::warning
+The Euro Office project is currently in its early stages and may have stability issues.
+:::
+
+## What you will find here
+
+- Set up Euro Office with OpenCloud using Docker Compose.
+- Configure Euro Office behind an external Nginx reverse proxy.
+
+## Docker Compose Setup
+
+Euro Office is available as a compose module in the [opencloud-compose](https://github.com/opencloud-eu/opencloud-compose) project.
+
+### With Traefik (built-in reverse proxy)
+
+Set the following in your `.env` file:
+
+```env
+COMPOSE_FILE=docker-compose.yml:weboffice/euroffice.yml:traefik/opencloud.yml:traefik/euroffice.yml
+
+EURO_OFFICE_DOMAIN=euro-office.YOUR.DOMAIN
+EURO_OFFICE_WOPISERVER_DOMAIN=wopiserver-eo.YOUR.DOMAIN
+EURO_OFFICE_JWT_SECRET=YOUR.SECRET
+```
+
+### With an external proxy (Nginx, Caddy, etc.)
+
+Set the following in your `.env` file:
+
+```env
+COMPOSE_FILE=docker-compose.yml:weboffice/euroffice.yml:external-proxy/opencloud.yml:external-proxy/euroffice.yml
+
+EURO_OFFICE_DOMAIN=euro-office.YOUR.DOMAIN
+EURO_OFFICE_WOPISERVER_DOMAIN=wopiserver-eo.YOUR.DOMAIN
+EURO_OFFICE_JWT_SECRET=YOUR.SECRET
+```
+
+For the full Nginx configuration guide, see [Behind External Proxy](../../getting-started/container/docker-compose/external-proxy).
+
+### Using both Collabora and Euro Office
+
+Both office suites can run simultaneously. In this case, OpenDocument formats (`.odt`, `.ods`, `.odp`) open in Collabora while Microsoft Office formats (`.docx`, `.xlsx`, `.pptx`) open in Euro Office.
+
+:::info
+To avoid app interlocking issues, be aware that there is currently no cross-app file locking. If a file is opened in one app, the other app must wait for the lock to be released.
+:::
+
+With Traefik:
+
+```env
+COMPOSE_FILE=docker-compose.yml:weboffice/collabora.yml:weboffice/euroffice.yml:traefik/opencloud.yml:traefik/collabora.yml:traefik/euroffice.yml
+```
+
+With external proxy:
+
+```env
+COMPOSE_FILE=docker-compose.yml:weboffice/collabora.yml:weboffice/euroffice.yml:external-proxy/opencloud.yml:external-proxy/collabora.yml:external-proxy/euroffice.yml
+```
+
+## Environment Variables
+
+| Variable | Default | Description |
+|---|---|---|
+| `EURO_OFFICE_DOMAIN` | `euro-office.opencloud.test` | Domain of the Euro Office document server |
+| `EURO_OFFICE_WOPISERVER_DOMAIN` | `wopiserver-eo.opencloud.test` | Domain of the WOPI server for Euro Office |
+| `EURO_OFFICE_JWT_SECRET` | `changeme` | JWT secret for Euro Office. **Change this for production!** |
+| `EURO_OFFICE_DOCKER_IMAGE` | `ghcr.io/euro-office/documentserver` | Docker image for the document server |
+| `EURO_OFFICE_DOCKER_TAG` | `latest` | Docker image tag |
+
+## Exposed Ports (External Proxy)
+
+When using an external reverse proxy, the following ports are exposed on the host:
+
+| Service | Host Port | Description |
+|---|---|---|
+| Euro Office Document Server | `9900` | The document editing interface |
+| Euro Office WOPI Server | `9302` | WOPI protocol endpoint (collaboration service) |
+
+## DNS Entries
+
+When deploying with custom domains, make sure DNS records point to your server for:
+
+- `euro-office.YOUR.DOMAIN`
+- `wopiserver-eo.YOUR.DOMAIN`
+
+For local testing with `.test` domains, add to `/etc/hosts`:
+
+```text
+127.0.0.1 euro-office.opencloud.test
+127.0.0.1 wopiserver-eo.opencloud.test
+```