refactor(providers): clean up config structure and update PackyCode domain

- Remove redundant 'config' field from Claude default configuration
  * Align with SSOT architecture where Claude only requires 'env' field
  * Matches the actual structure used in settings.json

- Update PackyCode provider configuration
  * Migrate domain: packycode.com → packyapi.com
  * Update API endpoints to new domain structure
  * Update load balancer endpoint: api-slb.packycode.com → api-slb.packyapi.com

src/components/providers/forms/ProviderForm.tsx

@@ -36,7 +36,7 @@ import {
   useCodexTomlValidation,
 } from "./hooks";
 
-const CLAUDE_DEFAULT_CONFIG = JSON.stringify({ env: {}, config: {} }, null, 2);
+const CLAUDE_DEFAULT_CONFIG = JSON.stringify({ env: {} }, null, 2);
 const CODEX_DEFAULT_CONFIG = JSON.stringify({ auth: {}, config: "" }, null, 2);
 
 type PresetEntry = {