[Fix] Unify all instances of fetching the production URL

[dcshzj]

There are 3 instances in which the production URL can be obtained:

1. src/hooks/useSiteUrlHook.jsx - very legacy code that uses local storage, should be removed after it is confirmed that there are no usages
2. src/hooks/settingsHooks/useUrlHook.jsx - somewhat legacy code, used on the Settings page, should be replaced because it uses a user-defined value
3. src/hooks/settingsHooks/useGetSiteUrl.ts - newest code introduced as part of review requests, should be updated to use the new /v2/sites/:siteName/siteUrl endpoint.

All usages should be consolidated into the 3rd version for consistency.