feat(site): merge /anti-patterns and /visual-mode into /slop

Top nav was at six items and growing. The anti-patterns catalog and the
visual-mode overlay demo were always two views of the same subject (the
rule set and seeing it caught in place), so collapsing them into one page
reduces nav weight and puts the catalog + live demo next to each other.

Four sections in one scroll: See it (iframe demo), Try it live (specimen
gallery), The catalog (full rule list), Run it yourself (invocation
methods). Sidebar TOC nests the catalog sections under "The catalog" for
deep linking. 301s from the old URLs preserve external links.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/lib/render-page.js

@@ -33,7 +33,7 @@ export function readHeaderPartial() {
  * the default nav href state. Matches on `data-nav="{activeNav}"`.
  *
  * @param {string} headerHtml
- * @param {string} activeNav - one of: home, skills, anti-patterns, tutorials, gallery, github
+ * @param {string} activeNav - one of: home, designing, docs, slop, live, github
  * @returns {string}
  */
 export function applyActiveNav(headerHtml, activeNav) {