Describe the Bug

admin.meta.title accepts Metadata['title'] from Next.js, which includes the object form { default, template }. However, passing an object results in [object Object] being rendered in the browser tab title.

The issue is in packages/next/src/utilities/meta.ts#L46-L48:

const metaTitle: Metadata['title'] = [incomingMetadata.title, titleSuffix]
  .filter(Boolean)
  .join(' ')

.join(' ') stringifies the title object to [object Object]. The same issue applies to the ogTitle computation on line 50.

Link to the code that reproduces this issue

https://github.com/payloadcms/payload/blob/main/packages/next/src/utilities/meta.ts#L46-L48

Reproduction Steps

1. Set admin.meta.title to a Next.js title object: { default: 'My CMS', template: '%s | My CMS' }
2. Start the dev server
3. Open the admin dashboard
4. Browser tab shows [object Object] - Payload

Which area(s) are affected?

area: ui

Environment Info

Payload 3.78.0, Next.js 15