TEST: Mentor availability change via profile update

[nora-weisser]

• Mentor availability is changed by updating menteeSection.longTerm and/or menteeSection.adHoc through PUT /api/platform/v1/mentors/{id} (permission MENTOR_PROFILE_UPDATE). No dedicated toggle endpoint exists.
• A long-term mentor adding adHoc availability immediately appears under ?mentorshipTypes=AD_HOC.
• Removing longTerm while keeping adHoc immediately removes the mentor from ?mentorshipTypes=LONG_TERM.
• validateMentorCommitment re-runs on every update — same hoursPerMentee >= 2 rule.