Use mcdsl/terminal for all password prompts

Replace direct golang.org/x/term calls with mcdsl/terminal.ReadPassword
across mciasctl (6 sites), mciasgrpcctl (1 site), and mciasdb (1 site).
Aligns with the new CLI security standard in engineering-standards.md.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/modernc.org/libc/AUTHORS

@@ -17,6 +17,7 @@ Jason DeBettencourt <jasond17@gmail.com>
 Jasper Siepkes <jasper@siepkes.nl>
 Koichi Shiraishi <zchee.io@gmail.com>
 Marius Orcsik <marius@federated.id>
+Olivier Mengué <dolmen@cpan.org>
 Patricio Whittingslow <graded.sp@gmail.com>
 Scot C Bontrager <scot@indievisible.org>
 Steffen Butzer <steffen(dot)butzer@outlook.com>