fix(security): keep database passwords out of every argv

MariaDB dumps and restores read the password from MYSQL_PWD, and docker exec forwards env variables by name only, so no process listing shows a password. baudolo-restore gains --db-password-stdin; --db-password still works but warns.

🎯 Fix: 96 %
💥 Break: 3 %
💸 Cost: –
⏱️ Time: –
🛡️ Security: ~100 %
🏆 Score: 93
🚦 Gate: ✅ 90/5, cost and time <= 100, security 100 %

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/e2e/test_e2e_postgres_full.py

@@ -94,7 +94,7 @@ class TestE2EPostgresFull(unittest.TestCase):
         )
 
         # Restore
-        run(
+        cls.restored = run(
             [
                 "baudolo-restore",
                 "postgres",
@@ -129,6 +129,9 @@ class TestE2EPostgresFull(unittest.TestCase):
         )
         self.assertTrue(p.is_file(), f"Expected dump file at: {p}")
 
+    def test_the_deprecated_password_argument_still_restores_but_warns(self) -> None:
+        self.assertIn("visible in the process list", self.restored.stderr)
+
     def test_data_restored(self) -> None:
         p = run(
             [