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/google.golang.org/grpc/internal/buffer/unbounded.go

@@ -83,6 +83,7 @@ func (b *Unbounded) Load() {
 		default:
 		}
 	} else if b.closing && !b.closed {
+		b.closed = true
 		close(b.c)
 	}
 }