refactor: remove required constraints and empty API key fields

- Remove 'required' attribute from Codex auth.json textarea
- Remove conditional 'required' logic from API key input field
- Clean up Codex Official preset by removing null OPENAI_API_KEY entry
- Allow more flexible form validation while maintaining backend checks

src/components/providers/forms/CodexConfigSections.tsx

@@ -35,7 +35,6 @@ export const CodexAuthSection: React.FC<CodexAuthSectionProps> = ({
         onBlur={onBlur}
         placeholder={t("codexConfig.authJsonPlaceholder")}
         rows={6}
-        required
         className="w-full px-3 py-2 border border-border-default  dark:bg-gray-800 dark:text-gray-100 rounded-lg text-sm font-mono focus:outline-none focus:ring-2 focus:ring-blue-500/20 dark:focus:ring-blue-400/20  transition-colors resize-y min-h-[8rem]"
         autoComplete="off"
         autoCorrect="off"