feat(20-02): add updateMemberProfile fetcher + AdminMember.isAdmin
- Add isAdmin: boolean to AdminMember interface (after color, before
hasCredential) — feeds the Phase 20 editor toggle initial state (D-02)
- Add updateMemberProfile(memberId, body) fetcher: PATCH /api/admin/members/:id,
credentials:include, redirect:manual, JSON body
- Maps 401/opaqueredirect → SessionExpiredError (existing convention)
- Maps 409/422 → Error('last-admin') sentinel (D-03 last-admin guard)
- Maps other non-ok → generic error
- All 50 tests pass; eslint + prettier + tsc --noEmit exit 0
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
