Adds a project-centric ops view for mentor management:
- New mentor.getMenteeActivity tRPC procedure aggregates every project
with wantsMentorship=true and derives a status (unassigned / assigned
/ active / stalled) from the latest message + file activity.
- /admin/mentors becomes a tabbed page: existing Mentor list +
new Mentees & Activity table with status pills, search, and a
per-row Assign/Open CTA linking to /admin/projects/[id]/mentor.
- Includes 2 unit tests covering classification + program scoping.
Also: ignore .remember/ (plugin scratch dir).
