fix: render preview modal via React portal to escape navbar stacking context

The navbar uses backdrop-blur-md which creates a CSS stacking context.
Any position:fixed child is clipped to that context instead of the
viewport, making the modal invisible. Using createPortal to mount the
modal directly on document.body ensures it always renders above
everything regardless of ancestor transforms or filters.

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

Author: amide-init

src/components/PortfolioPreviewModal.tsx

@@ -1,4 +1,5 @@
 import { useEffect, useRef } from 'react'
+import { createPortal } from 'react-dom'
 import { X, Star, MapPin, Globe, ExternalLink, GitFork, Users, BookOpen } from 'lucide-react'
 
 // Twitter/X brand icon (lucide-react does not ship it)
@@ -164,7 +165,7 @@ export function PortfolioPreviewModal({ user, repos, onClose }: Props) {
     ? user.blog.startsWith('http') ? user.blog : `https://${user.blog}`
     : null
 
-  return (
+  return createPortal(
     <div
       className="fixed inset-0 z-[200] flex flex-col bg-black/70 backdrop-blur-sm"
       role="dialog"
@@ -366,6 +367,7 @@ export function PortfolioPreviewModal({ user, repos, onClose }: Props) {
         </section>
 
       </div>
-    </div>
+    </div>,
+    document.body
   )
 }