test(e2e): add dump-only-sql mixed-run + CLI contract coverage

- rename dump-only flag to --dump-only-sql across docs and tests
- update backup logic: skip files/ only for DB volumes when dumps succeed; fallback to files when dumps fail
- extend e2e helpers to support dump_only_sql
- add e2e mixed-run regression test (DB dump => no files/, non-DB => files/)
- add e2e CLI/argparse contract test (--dump-only-sql present, --dump-only rejected)
- fix e2e files test to expect file backups for non-DB volumes in dump-only-sql mode and verify restore
- update changelog + README flag table

https://chatgpt.com/share/69522d9c-ce08-800f-9070-71df3bd779ae

tests/e2e/test_e2e_dump_only_fallback_to_files.py

@@ -19,7 +19,7 @@ class TestE2EDumpOnlyFallbackToFiles(unittest.TestCase):
     @classmethod
     def setUpClass(cls) -> None:
         require_docker()
-        cls.prefix = unique("baudolo-e2e-dump-only-fallback")
+        cls.prefix = unique("baudolo-e2e-dump-only-sql-fallback")
         cls.backups_dir = f"/tmp/{cls.prefix}/Backups"
         ensure_empty_dir(cls.backups_dir)
 
@@ -57,7 +57,7 @@ class TestE2EDumpOnlyFallbackToFiles(unittest.TestCase):
         wait_for_postgres(cls.pg_container, user="postgres", timeout_s=90)
 
         # Add a deterministic marker file into the volume
-        cls.marker = "dump-only-fallback-marker"
+        cls.marker = "dump-only-sql-fallback-marker"
         run(
             [
                 "docker",
@@ -73,7 +73,7 @@ class TestE2EDumpOnlyFallbackToFiles(unittest.TestCase):
         cls.databases_csv = f"/tmp/{cls.prefix}/databases.csv"
         write_databases_csv(cls.databases_csv, [])  # empty except header
 
-        # Run baudolo with --dump-only and a DB container present:
+        # Run baudolo with --dump-only-sql and a DB container present:
         # Expected: WARNING + FALLBACK to file backup (files/ must exist)
         cmd = [
             "baudolo",
@@ -94,7 +94,7 @@ class TestE2EDumpOnlyFallbackToFiles(unittest.TestCase):
             "mariadb",
             "mysql",
             "alpine",
-            "--dump-only",
+            "--dump-only-sql",
         ]
         cp = run(cmd, capture=True, check=True)
 
@@ -127,7 +127,7 @@ class TestE2EDumpOnlyFallbackToFiles(unittest.TestCase):
 
     def test_warns_about_missing_dump_in_dump_only_mode(self) -> None:
         self.assertIn(
-            "WARNING: dump-only requested but no DB dump was produced",
+            "WARNING: dump-only-sql requested but no DB dump was produced",
             self.stdout,
             f"Expected warning in baudolo output. STDOUT:\n{self.stdout}",
         )