Fix mRemoteNG import failing on entries without a username

The previous username relaxation only touched ProfileDialog's own
save-time validation. ProfileRepository::isProfileValid() had the
identical "username required for SSH/RDP" check independently, called
directly by insertProfile()/updateProfile() -- exactly the path
mRemoteNG import uses, since it builds Profile objects and inserts
them directly rather than going through the dialog. Every imported
SSH/RDP entry without a recorded username was rejected outright.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/profile_repository.cpp

@@ -235,13 +235,6 @@ bool isProfileValid(const Profile& profile, QString* error)
     }
 
     const QString protocol = normalizedProtocol(profile.protocol);
-    if ((protocol == QStringLiteral("SSH") || protocol == QStringLiteral("RDP"))
-        && profile.username.trimmed().isEmpty()) {
-        if (error != nullptr) {
-            *error = QStringLiteral("Username is required for %1 profiles.").arg(protocol);
-        }
-        return false;
-    }
 
     const QString authMode = normalizedAuthMode(protocol, profile.authMode);
     if (protocol == QStringLiteral("SSH") && authMode == QStringLiteral("Private Key")