fix(backup)!: read the instance from one engine-name set, and trust it

Two shapes fell through the inline regex, which knew `database`, `db` and
`postgres` only. A container named exactly after its engine - what a compose
file writes as `container_name: postgres` - carries no separator before the
token, so it resolved to nothing and 6.0.0 stopped dumping it without saying
so. And a swarm task of a central MariaDB reads `mariadb_mariadb.1.<id>`,
where `_mariadb` was no token at all, so that database has never been dumped
under swarm at all.

ENGINE_NAMES states the set once and serves both readings: carried as a
suffix it makes the rest the instance, being one outright makes the container
its own instance.

backup_mariadb_or_postgres stops calling an application container a database.
container_engine recognises an engine by its client tools, which an
application image often ships, so refusing the dump alone would have recorded
the volume as `database: true, dumped: false` - the exact shape a restore
drill reads as a database that was missed. Without an instance there is no
database to record.

BREAKING CHANGE: `mariadb` and `mysql` join the suffix tokens, so a container
named `<app>-mariadb` resolves to the instance `<app>` rather than to its own
name. A databases.csv keyed on the full container name has to move to the
application name, or name the container in --database-containers.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/baudolo/backup/dumps.py

@@ -10,7 +10,7 @@ from pandas.errors import EmptyDataError
 
 from baudolo.databases import COLUMNS, DELIMITER
 
-from .db import backup_database
+from .db import backup_database, get_instance
 from .docker import has_tool, image_id
 
 DUMP_TOOLS: tuple[tuple[str, str], ...] = (
@@ -76,6 +76,8 @@ def backup_mariadb_or_postgres(
     engine = container_engine(container)
     if engine is None:
         return VolumeOutcome(database=False, dumped=False)
+    if get_instance(container, database_containers) is None:
+        return VolumeOutcome(database=False, dumped=False)
     db_type, dump_tool = engine
     dumped = backup_database(
         container=container,