fix: include standard mime.types in nginx config

The custom types block replaced all default MIME types, causing
index.html to be served as application/octet-stream. Include the
system mime.types and only add the custom .rpm type on top.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

asset/nginx/rpm.lair.cafe.conf

@@ -10,9 +10,9 @@ server {
 
     root /var/www/rpm;
 
+    include /etc/nginx/mime.types;
     types {
         application/x-rpm rpm;
-        application/xml xml;
     }
     default_type application/octet-stream;