feat: PostgreSQL driver support

docs/docker.md

@@ -102,6 +102,17 @@ To use MariaDB, change the `mysql` service image to `mariadb:11`, its `MYSQL_*`
 
 Back the database up with `docker compose -f docker-compose.mysql.yml exec mysql mysqldump ...` (a `tar` copy of the volume is not consistent while it runs), and the `renewcms-data` volume as described above. Moving an existing SQLite volume is a manual procedure, see [deployment.md](deployment.md#moving-an-existing-sqlite-site-to-mysql).
 
+## PostgreSQL
+
+[`docker-compose.postgres.yml`](../docker-compose.postgres.yml) runs RenewCMS next to a PostgreSQL 17 container:
+
+```sh
+export DB_PASSWORD=<generated>
+docker compose -f docker-compose.postgres.yml up -d
+```
+
+It starts the `postgres` service with a named volume `postgres-data` and a `pg_isready` healthcheck, and starts `renewcms` only once the database is healthy (`depends_on` with `service_healthy`). RenewCMS gets `DB_DRIVER=postgres`, `DB_HOST=postgres`, `DB_PORT`, `DB_NAME`, `DB_USER`, `DB_PASSWORD` and `DB_SSLMODE=disable` (the traffic stays on the Compose network) from the compose file and the rest from `docker.env`. `DATA_DIR=/data` keeps update state and the `.sql` pre-update backups on the `renewcms-data` volume. For a server on another machine drop the `postgres` service, point `DB_HOST` at it and set `DB_SSLMODE=require`. Back the database up with `docker compose -f docker-compose.postgres.yml exec postgres pg_dump -U renewcms renewcms`. Replace the placeholders; never commit real passwords.
+
 ## S3-compatible storage (SeaweedFS)
 
 [`docker-compose.s3.yml`](../docker-compose.s3.yml) runs RenewCMS with `STORAGE_DRIVER=s3` next to a [SeaweedFS](https://github.com/seaweedfs/seaweedfs) server (Apache 2.0, image `chrislusf/seaweedfs`, override with `SEAWEEDFS_IMAGE`) with its S3 gateway enabled, and a one-shot `seaweedfs-init` step that creates the bucket with `weed shell`: