fix: security hardening — block self-registration, SSE auth, audit logging fixes

Security fixes:
- Block self-registration via magic link (PrismaAdapter createUser throws)
- Magic links only sent to existing ACTIVE users (prevents enumeration)
- signIn callback rejects non-existent users (defense-in-depth)
- Change schema default role from JURY_MEMBER to APPLICANT
- Add authentication to live-voting SSE stream endpoint
- Fix false FILE_OPENED/FILE_DOWNLOADED audit events on page load
  (remove purpose from eagerly pre-fetched URL queries)

Bug fixes:
- Fix impersonation skeleton screen on applicant dashboard
- Fix onboarding redirect loop in auth layout

Observer dashboard redesign (Steps 1-6):
- Clickable round pipeline with selected round highlighting
- Round-type-specific dashboard panels (intake, filtering, evaluation,
  submission, mentoring, live final, deliberation)
- Enhanced activity feed with server-side humanization
- Previous round comparison section
- New backend queries for round-specific analytics

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

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

@@ -62,7 +62,7 @@ export default function ApplicantDashboardPage() {
     enabled: isAuthenticated,
   })
 
-  if (sessionStatus === 'loading' || isLoading) {
+  if (sessionStatus === 'loading' || (isAuthenticated && isLoading)) {
     return (
       <div className="space-y-6">
         <div className="space-y-2">