Describe the Bug

b82356b updates all calls to formatAdminURL() to pass in config.serverURL. When I set serverURL: "http://localhost:3000", run npm run dev and go to http://localhost:3000/admin, I get the error

 ⨯ [TypeError: Invalid URL] {
  code: 'ERR_INVALID_URL',
  input: 'http://localhost:3000http://localhost:3000/admin',
  digest: '185251315'
}
[12:26:08] ERROR: Failed to create URL object from URL: http://localhost:3000http://localhost:3000/admin, falling back to http://localhost:3000http://localhost:3000/admin

It seems the function formatAdminURL() is also being used to get the path of routes, not just the absolute URL, so the commit breaks all of those cases if serverURL is set:

Here, currentRoute is supposed to be the admin route, e.g., "/admin", but by passing in a set serverURL, it is now "http://localhost:3000/admin". Later on, in the same component:

urlSuffix is now "http://localhost:3000/admin", and this breaks createLocalReq(), which basically tries to construct the URL `http://localhost:3000http://localhost:3000/admin"

Link to the code that reproduces this issue

N/A

Reproduction Steps

• Run npx create-payload-app@latest -t blank with SQLite driver
• Set serverURL: "http://localhost:3000", in payload.config.ts
• Run npm run dev
• Go to http://localhost:3000/admin

Which area(s) are affected?

area: core

Environment Info

Relevant Packages:
  payload: 3.68.3
  next: 15.5.9
  @payloadcms/db-postgres: 3.68.3
  @payloadcms/drizzle: 3.68.3
  @payloadcms/graphql: 3.68.3
  @payloadcms/next/utilities: 3.68.3      
  @payloadcms/plugin-cloud-storage: 3.68.3
  @payloadcms/storage-s3: 3.68.3
  @payloadcms/translations: 3.68.3       
  @payloadcms/ui/shared: 3.68.3
  react: 19.2.1
  react-dom: 19.2.1
Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 10 Pro