UI/UX audit fixes: clickable pipelines, broken links, isActive locking

- Make pipeline cards clickable on list page (navigate to detail view)
- Fix broken nav link: applicant /messages → /mentor
- Fix broken nav link: mentor /messages → /projects
- Add isActive field locking to all 7 wizard sections (intake, main-track,
  filtering, assignment, awards, live-finals, notifications)
- Add minLoad ≤ maxLoad cross-field validation in assignment section
- Add duplicate stage slug detection in main track section
- Add active pipeline warning banners in intake and main track sections

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/(applicant)/applicant/pipeline/page.tsx

@@ -250,7 +250,7 @@ export default function ApplicantPipelinePage() {
           </div>
         </Link>
         <Link
-          href={"/applicant/messages" as Route}
+          href={"/applicant/mentor" as Route}
           className="group flex items-center gap-3 rounded-xl border p-4 transition-all hover:border-amber-500/30 hover:bg-amber-50/50 hover:-translate-y-0.5 hover:shadow-md"
         >
           <div className="rounded-lg bg-amber-50 p-2 dark:bg-amber-950/40">