TEST: Mentor profile update

[nora-weisser]

• PUT /api/platform/v1/mentors/{id} requires permission MENTOR_PROFILE_UPDATE.
• The DTO merges into the persisted mentor; verify that omitted fields keep their stored value and present fields overwrite.
• URL formats (Calendly, LinkedIn) re-validated on update.
• updated_at advances on every successful update.
• Updated profile is immediately reflected on the public list and the admin portal.