fix: use credential-prototype:import-json in postinst instead of sync

Explicitly import mserver.credprototype.json by path so only this
package's prototype is registered, rather than syncing all prototypes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Vitexus

debian/multiflexi-mserver.postinst

@@ -5,7 +5,7 @@ set -e
 case "$1" in
     configure)
         if [ -x /usr/bin/multiflexi-cli ]; then
-            multiflexi-cli credential-prototype:sync
+            multiflexi-cli credential-prototype:import-json --file /usr/lib/multiflexi-mserver/multiflexi/mserver.credprototype.json
         fi
         ;;