Wrong Error message when invitee email address unverified

**Describe the bug**

- In self-deployment, the user emails in Authgear portal (`accounts`) may left unverified due to the lack of email server. The admin may choose to manually verify the email offline instead.
- When an invitation link to a project is accepted by a user, they will see "The invitee email does not match your logged in email", while the email address is actually correct


**Todo**

- Return a correct error message here
> ## Email address must be verified
> Your email address must be verified to accept the invitation. Please contact admin to verify your email address.
> [Login as another user]

The issue names no files, tests, or entry points. Trace the project invitation acceptance flow to the current email-mismatch error, then verify the unverified-email case and update the result to the specified message; add or adjust coverage if the relevant test area is found.

Written by the indexing model from the issue text.