fix: use expanded regex in nginx location for hashed assets

Replace {8} quantifier with 8 repeated character classes for
compatibility with nginx regex parsing.

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

nginx.conf

@@ -38,7 +38,7 @@ server {
     }
 
     # Hashed static assets — long-term cache is safe
-    location ~* \.[0-9a-f]{8}\.(js|css)$ {
+    location ~* \.[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]\.(js|css)$ {
         expires 30d;
         add_header Cache-Control "public, immutable";
     }