refactor: extract API Key link and custom endpoints logic into hooks

- Create useApiKeyLink hook to manage API Key retrieval link display and URL
- Create useCustomEndpoints hook to collect endpoints from multiple sources
- Simplify ProviderForm by using these new hooks
- Reduce code duplication and improve maintainability
- Fix TypeScript error with form.watch("websiteUrl") by providing default empty string

src/components/providers/forms/hooks/index.ts

@@ -3,3 +3,5 @@ export { useApiKeyState } from "./useApiKeyState";
 export { useBaseUrlState } from "./useBaseUrlState";
 export { useModelState } from "./useModelState";
 export { useCodexConfigState } from "./useCodexConfigState";
+export { useApiKeyLink } from "./useApiKeyLink";
+export { useCustomEndpoints } from "./useCustomEndpoints";