chore(config): drop dead Netdata/code-server links and unused URL constants

Netdata was never deployed and code-server was decommissioned on
2026-07-19; their quick links pointed at dead domains. The
portainerUrl/netdataUrl constants had no consumers (quick links
hardcode their own URLs). The Portainer quick link stays — its
portainer.schweitz.net host arrives with the port-lockdown phase.

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

lib/core/config/app_config.dart

@@ -67,15 +67,4 @@ class AppConfig {
       coreApiUrl.contains('schweitz.net') ||
       tatlockApiUrl.contains('schweitz.net');
 
-  /// Portainer URL for container management
-  static const portainerUrl = String.fromEnvironment(
-    'PORTAINER_URL',
-    defaultValue: 'http://192.168.86.149:9000',
-  );
-
-  /// Netdata URL for system monitoring
-  static const netdataUrl = String.fromEnvironment(
-    'NETDATA_URL',
-    defaultValue: 'http://192.168.86.149:19999',
-  );
 }