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/shared/ApiKeySection.tsx

@@ -48,7 +48,6 @@ export function ApiKeySection({
         label={label}
         value={value}
         onChange={onChange}
-        required={category !== "official"}
         placeholder={
           category === "official"
             ? finalPlaceholder.official