feat(seed): read the database password from stdin with --password-stdin

baudolo-seed took the database password only as a positional argument, so it showed in the process list of the host that seeds the backup catalog (infinito-nexus/core #1213). --password-stdin reads it from stdin without the trailing newline. The positional argument still works for existing callers but warns on stderr that it is visible in the process list; giving the password both ways, or neither, is rejected with a usage error and writes nothing.

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

tests/unit/seed/test_main.py

@@ -164,6 +164,7 @@ class TestSeedMain(unittest.TestCase):
         ns.database = "db"
         ns.username = "user"
         ns.password = "pass"
+        ns.password_stdin = False
         parse_args.return_value = ns
 
         seed_main.main()
@@ -195,6 +196,7 @@ class TestSeedMain(unittest.TestCase):
         ns.database = "db"
         ns.username = "user"
         ns.password = "pass"
+        ns.password_stdin = False
         parse_args.return_value = ns
 
         seed_main.main()