feat(admin-teams): GET team members endpoint with last_active_at

[sage-ali]

Context

Derived from the audit in #205. Depends on #229 (admin_auth_metadata.last_active_at must exist and be populated before this endpoint can return meaningful data).

No endpoint exists to list who is currently on the admin team. This is the last missing piece of the team management surface.

What's needed

GET /admin/teams/:teamId/members

Paginated list of current team members.

Response shape per member:

{
  id: string           // team_memberships.id
  user_id: string
  full_name: string    // from users
  email: string        // from users
  role: string         // from team_memberships
  joined_at: Date      // from team_memberships
  last_active_at: Date | null  // from admin_auth_metadata
}

Query params: page, limit (via existing PaginationDto)

Implementation:

• Query builder joining team_memberships → users → admin_auth_metadata (LEFT JOIN on admin_auth_metadata — member may not have one yet if they've never made a request)
• Order by joined_at DESC by default
• Scoped to members where users.is_active = true and users.deleted_at IS NULL

TeamMembersListAction

Raw query builder action (similar pattern to AdminUsersListAction) rather than going through AbstractModelAction — the three-table join with a nullable left join makes the generic API awkward here.

Acceptance criteria

• Returns paginated list of active team members
• last_active_at is null for members who have never made an authenticated admin request
• Soft-deleted or inactive users are excluded
• Response matches the shape above
• Swagger doc added

Depends on

#229