fix(final-docs): exclude dropped mentors from doc access; relative in-app reminder link

Review follow-ups: mentor.getProjectFinalDocuments now filters droppedAt:null
(a dropped mentor no longer sees a team's final docs); reminder linkUrl is
relative so the in-app notification does client-side nav (email still absolutized).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/server/routers/mentor.ts

@@ -223,7 +223,7 @@ export const mentorRouter = router({
       const isAdmin = ['SUPER_ADMIN', 'PROGRAM_ADMIN'].includes(ctx.user.role)
       if (!isAdmin) {
         const [mentorAssignment, teamMembership] = await Promise.all([
-          ctx.prisma.mentorAssignment.findFirst({ where: { mentorId: ctx.user.id, projectId: input.projectId }, select: { id: true } }),
+          ctx.prisma.mentorAssignment.findFirst({ where: { mentorId: ctx.user.id, projectId: input.projectId, droppedAt: null }, select: { id: true } }),
           ctx.prisma.teamMember.findFirst({ where: { userId: ctx.user.id, projectId: input.projectId }, select: { id: true } }),
         ])
         if (!mentorAssignment && !teamMembership) throw new TRPCError({ code: 'FORBIDDEN', message: 'No access to this project' })