Use mcdsl/terminal.ReadPassword for secure password input

Replaces raw bufio.Scanner password reading (which echoed to terminal)
with the new mcdsl terminal package that suppresses echo via x/term.

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

vendor/modules.txt

@@ -2,6 +2,9 @@
 ## explicit; go 1.25.7
 git.wntrmute.dev/mc/mc-proxy/client/mcproxy
 git.wntrmute.dev/mc/mc-proxy/gen/mc_proxy/v1
+# git.wntrmute.dev/mc/mcdsl v1.3.0
+## explicit; go 1.25.7
+git.wntrmute.dev/mc/mcdsl/terminal
 # github.com/dustin/go-humanize v1.0.1
 ## explicit; go 1.16
 github.com/dustin/go-humanize
@@ -43,8 +46,12 @@ golang.org/x/net/internal/timeseries
 golang.org/x/net/trace
 # golang.org/x/sys v0.42.0
 ## explicit; go 1.25.0
+golang.org/x/sys/plan9
 golang.org/x/sys/unix
 golang.org/x/sys/windows
+# golang.org/x/term v0.41.0
+## explicit; go 1.25.0
+golang.org/x/term
 # golang.org/x/text v0.32.0
 ## explicit; go 1.24.0
 golang.org/x/text/secure/bidirule