refactor button elements; change button types for search and filter actions in admin pages

src/routes/admin.js

@@ -78,11 +78,14 @@ async function adminRoutes(fastify) {
   });
 
   // static assets (css + js) under /admin/assets/*
+  // use must-revalidate so the browser always checks for a newer copy;
+  // prevents the admin getting stuck on old js after a deploy.
   fastify.register(fastifyStatic, {
     root: assetsDir,
     prefix: '/admin/assets/',
     decorateReply: false,
-    cacheControl: false,
+    cacheControl: true,
+    maxAge: 0,
   });
 
   // top-level entry — redirect to articles