feat(backup)!: mandatory repo-name and databases-csv, --only-files, --only-sql

Two defaults could not be right. --repo-name fell back to the literal 'backup-docker-to-local' while its help promised the git repo folder name, which nothing ever derived. --databases-csv pointed inside the installed package directory, where credentials must not live; when it applied, load_databases_df read a missing file as empty and the run finished without a single dump and without an error. Both are required now, --repo-name in the restore CLI too. The file itself may still be absent - babadcb's tolerance is untouched, only the path must be named.

--everything is withdrawn. Its one effect was to ignore --images-no-stop-required, which is what leaving that list empty already does, and its branch was the default path minus the requires_stop check. No caller, no test, and help and README described it differently.

--dump-only-sql becomes --only-sql, and --only-files joins it as the opposite half: no dumps at all, every volume as files. They form a mutually exclusive group. A host that only copies files has no business holding database passwords, so --databases-csv is not required there and is never read.

The smallest valid argv turned out to be written four times across the test tree; it now lives once. Withdrawn flags are listed in one place and proven to exit 2.

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

tests/e2e/test_e2e_postgres_no_copy.py

@@ -76,7 +76,7 @@ class TestE2EPostgresNoCopy(unittest.TestCase):
             databases_csv=cls.databases_csv,
             database_containers=[cls.pg_container],
             images_no_stop_required=[POSTGRES_IMAGE],
-            dump_only_sql=True,
+            only_sql=True,
         )
 
         cls.hash, cls.version = latest_version_dir(cls.backups_dir, cls.repo_name)