fix: add copilot tests and lint fixes

src/agents/models-config.providers.ts

@@ -34,7 +34,7 @@ const MOONSHOT_DEFAULT_COST = {
 function normalizeApiKeyConfig(value: string): string {
   const trimmed = value.trim();
   const match = /^\$\{([A-Z0-9_]+)\}$/.exec(trimmed);
-  return match ? match[1] : trimmed;
+  return match?.[1] ?? trimmed;
 }
 
 function resolveEnvApiKeyVarName(provider: string): string | undefined {