refactor(ui): Relax static asset cache headers

Index now allows conditional revalidation so returning visitors reuse
the cached shell on 304s instead of re-downloading it every load.
Static assets cache for thirty days instead of a year, giving a sane
recovery window if a mishashed asset ever slips into a release.

Author: nfebe

nginx.conf

@@ -10,11 +10,11 @@ server {
 
     location / {
         try_files $uri $uri/ /index.html;
-        add_header Cache-Control "no-cache, no-store, must-revalidate";
+        add_header Cache-Control "no-cache";
     }
 
     location /assets/ {
-        expires 1y;
-        add_header Cache-Control "public, immutable";
+        expires 30d;
+        add_header Cache-Control "public";
     }
 }