feat: optional MySQL/MariaDB database driver for deployments that cannot use local SQLite

docs/deployment.md

@@ -8,7 +8,7 @@ RenewCMS ships as **one self-contained executable**. It serves:
 | `/healthz` | Liveness check, returns `200 ok`        |
 | `/*`       | The Vue SPA (embedded), with fallback to `index.html` for client-side routes |
 
-Runtime state includes the SQLite database (`DB_FILE`), uploads (`UPLOAD_DIR`), and update records, staged binaries and backups beside the database. Running a release binary needs no Go, Bun or Node installation. Browser updates additionally require Linux with systemd and the helper setup below.
+Runtime state includes the SQLite database (`DB_FILE`, or a MySQL/MariaDB server, see [Using MySQL or MariaDB](#using-mysql-or-mariadb)), uploads (`UPLOAD_DIR`), and update records, staged binaries and backups beside the database. Running a release binary needs no Go, Bun or Node installation. Browser updates additionally require Linux with systemd and the helper setup below.
 
 To run it in a container instead, see [docker.md](docker.md). The published image `git.floriansylvain.fr/fsylvain/renewcms` is upgraded with `docker compose pull && docker compose up -d`. Tags are `vX.Y.Z`, `X.Y.Z`, `X.Y` and `latest` for a stable release, and `vX.Y.Z-<pre>`, `X.Y.Z-<pre>` and the moving `<pre-name>` (`beta`, `rc`) for a pre-release, which never moves `latest`. Maintainers publish with `task docker:publish` after `docker login git.floriansylvain.fr`; there is no CI. See [Maintainer: publishing](docker.md#maintainer-publishing).
 
@@ -276,8 +276,37 @@ RenewCMS sends `Content-Security-Policy` (including `frame-ancestors 'none'`), `
 
 The CSP allows Google Fonts (`fonts.googleapis.com`, `fonts.gstatic.com`) and `https:` images, because the SPA loads its fonts from Google and articles may embed remote images. `style-src` keeps `'unsafe-inline'` for the article editor; `script-src` is `'self'` only.
 
+## Using MySQL or MariaDB
+
+SQLite is the default. To use an existing MySQL 8 or MariaDB 11 server instead, create an empty database and a user with full rights on it, then set in `/etc/renewcms/renewcms.env`:
+
+```sh
+DB_DRIVER=mysql
+DB_HOST=db.example.com
+DB_USER=renewcms
+DB_PASSWORD=<generated password>
+DB_NAME=renewcms
+DB_TLS=true
+DATA_DIR=/var/lib/renewcms
+```
+
+`DB_FILE` is then ignored. `DATA_DIR` is where update state, staged updates and backups live, so give it the same value as the helper's `--data-dir` (see [browser updates](#browser-updates)). Use `DB_TLS=true` (or `preferred`) whenever the server is not on the same host. Every variable is described in [configuration.md](configuration.md#database). The schema is created and migrated at startup, so the first start on an empty database needs nothing else.
+
+### Moving an existing SQLite site to MySQL
+
+There is no migration tool. The manual procedure, with the site stopped:
+
+1. Take a backup of the data directory (database file and uploads).
+2. Start RenewCMS once on the empty MySQL database so it creates the schema, then stop it.
+3. Export the rows from the SQLite file with `sqlite3 renewcms.db .dump`, keep only the `INSERT INTO` statements for `articles`, `images`, `users`, `invites`, `api_keys` and `purge_settings`, and import them into MySQL. Quoting and date formats differ between the two engines, so check a sample first: SQLite writes times such as `2026-01-02 03:04:05.123456789+00:00`, and the `+00:00` suffix must be removed for MariaDB and older MySQL versions. An unset time (`0001-01-01 00:00:00`) is valid as it is in MySQL and is read back as unset.
+4. Copy `uploads/` to the new `UPLOAD_DIR`, set `DB_DRIVER=mysql` and the connection variables, and start the service.
+
+Keep the SQLite file until you have checked the site.
+
 ## Backups
 
+With MySQL or MariaDB, back the database up with your server's own tools (for example `mysqldump --single-transaction`), plus the uploads directory. RenewCMS also writes a logical dump to `DATA_DIR/backups` before each update download. The rest of this section is about SQLite.
+
 Everything worth backing up is under the data directory. Take a consistent SQLite copy while the service is running:
 
 ```sh