feat(website): mirror index layout on category pages

Add search input, filter chips, no-results block, and back-to-top
button to category/group/subcategory pages. Pass filter_urls_json to
all page types so tag-chip navigation works site-wide. Fix JS so
filter-clear and no-results-clear redirect to / on non-index pages
instead of trying to filter a non-existent local table. Remove the
now-redundant .category-results CSS overrides.

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

website/static/main.js

@@ -341,6 +341,10 @@ tags.forEach(function (tag) {
 
 if (filterClear) {
   filterClear.addEventListener("click", function () {
+    if (!isIndexPage()) {
+      window.location.href = "/";
+      return;
+    }
     activeFilter = null;
     applyFilters();
   });
@@ -349,6 +353,10 @@ if (filterClear) {
 const noResultsClear = document.querySelector(".no-results-clear");
 if (noResultsClear) {
   noResultsClear.addEventListener("click", function () {
+    if (!isIndexPage()) {
+      window.location.href = "/";
+      return;
+    }
     if (searchInput) searchInput.value = "";
     activeFilter = null;
     applyFilters();
@@ -451,10 +459,8 @@ if (backToTop) {
   ) {
     activeSort = { col: sort, order: order };
   }
-  if (isIndexPage()) {
-    const matched = urlToFilter[location.pathname];
-    if (matched) activeFilter = matched;
-  }
+  const matched = urlToFilter[location.pathname];
+  if (matched) activeFilter = matched;
   if (q || activeFilter || sort) {
     sortRows();
   }

website/static/style.css

@@ -430,7 +430,7 @@ kbd {
 .tag:focus-visible,
 .back-to-top:focus-visible,
 .no-results-clear:focus-visible,
-.category-table a:focus-visible,
+.table a:focus-visible,
 .footer a:focus-visible,
 .sort-btn:focus-visible {
   outline: 2px solid var(--accent);
@@ -498,19 +498,6 @@ kbd {
   text-decoration-color: oklch(100% 0 0 / 0.7);
 }
 
-.category-results {
-  padding-top: clamp(2.5rem, 5vw, 3.75rem);
-}
-
-.category-results .results-intro {
-  grid-template-columns: 1fr;
-  gap: 0.6rem;
-}
-
-.category-results .results-intro .results-note {
-  justify-self: start;
-}
-
 .sponsor-band {
   padding-block: clamp(2.5rem, 5.5vw, 4rem);
   background: