Fix LDAP integration test: use GLAuth test credentials and runtime availability check

- Password "admin" → "password" (matches GLAuth config.toml)
- Replace hard Skip attribute with TCP connectivity check (test runs when GLAuth available)
- Add LdapSearchBase + AllowInsecureLdap to appsettings.Central.json for dev

src/ScadaLink.Host/appsettings.Central.json

@@ -24,6 +24,8 @@
       "LdapServer": "localhost",
       "LdapPort": 3893,
       "LdapUseTls": false,
+      "AllowInsecureLdap": true,
+      "LdapSearchBase": "dc=scadalink,dc=local",
       "JwtSigningKey": "CHANGE-ME-development-signing-key-at-least-32-chars",
       "JwtExpiryMinutes": 15,
       "IdleTimeoutMinutes": 30