feat(website): add entrance animations and CSS-based filter bar visibility

Replace hidden attribute on filter-bar with opacity/transform transition
driven by a .visible class, allowing smooth fade-in/slide-down when a
filter is active. Add staggered hero-in keyframe animations to the page
title, subtitle, action buttons, and search box. Polish sortable table
headers with color transition on hover and active states.

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

website/static/main.js

@@ -100,10 +100,10 @@ function applyFilters() {
   // Filter bar
   if (filterBar) {
     if (activeFilter) {
-      filterBar.hidden = false;
+      filterBar.classList.add('visible');
       if (filterValue) filterValue.textContent = activeFilter.value;
     } else {
-      filterBar.hidden = true;
+      filterBar.classList.remove('visible');
     }
   }