Consolidate skills from 21 to 18: rename, merge, and fold

- Rename /arrange to /layout for clarity
- Merge /normalize into /polish (design system discovery + cleanup phases)
- Merge /onboard into /harden (onboarding, empty states, progressive disclosure)
- Fold /extract into /impeccable extract sub-mode (reference file, sidebar link)
- Update all counts, cross-references, data files, demos, and metadata
- Remove System category (now empty)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/build-sub-pages.js

@@ -202,6 +202,7 @@ ${tutorials
     impeccable: [
       { id: 'impeccable-craft', label: '/impeccable craft', href: '/skills/impeccable#craft' },
       { id: 'impeccable-teach', label: '/impeccable teach', href: '/skills/impeccable#teach' },
+      { id: 'impeccable-extract', label: '/impeccable extract', href: '/skills/impeccable#extract' },
     ],
   };
 
@@ -280,7 +281,7 @@ ${skillChips}
   <header class="skills-overview-header">
     <p class="sub-page-eyebrow">${totalSkills} commands</p>
     <h1 class="sub-page-title">Skills</h1>
-    <p class="sub-page-lede">One skill, <a href="/skills/impeccable">/impeccable</a>, teaches your AI design. Twenty commands steer the result. Each command does one job with an opinion about what good looks like.</p>
+    <p class="sub-page-lede">One skill, <a href="/skills/impeccable">/impeccable</a>, teaches your AI design. Eighteen commands steer the result. Each command does one job with an opinion about what good looks like.</p>
   </header>
 
   <section class="skills-overview-howto">
@@ -632,7 +633,7 @@ export async function generateSubPages(rootDir) {
     const html = renderPage({
       title: 'Skills | Impeccable',
       description:
-        '21 commands that teach your AI harness how to design. Browse by category: create, evaluate, refine, simplify, harden, system.',
+        '18 commands that teach your AI harness how to design. Browse by category: create, evaluate, refine, simplify, harden.',
       bodyHtml: wrapInDocsLayout(sidebar, main),
       activeNav: 'docs',
       canonicalPath: '/skills',

scripts/lib/sub-pages-data.js

@@ -34,6 +34,10 @@ export {
 const EXCLUDED_SKILLS = new Set([
   'frontend-design',   // deprecated, renamed to impeccable
   'teach-impeccable',  // deprecated, folded into /impeccable teach
+  'arrange',           // renamed to layout
+  'normalize',         // merged into /polish
+  'onboard',           // merged into /harden
+  'extract',           // merged into /impeccable extract
 ]);
 
 /**
@@ -50,28 +54,24 @@ const SKILL_CATEGORIES = {
   audit: 'evaluate',
   // REFINE - improve existing design
   typeset: 'refine',
-  arrange: 'refine',
+  layout: 'refine',
   colorize: 'refine',
   animate: 'refine',
   delight: 'refine',
   bolder: 'refine',
   quieter: 'refine',
-  onboard: 'refine',
   overdrive: 'refine',
   // SIMPLIFY - reduce and clarify
   distill: 'simplify',
   clarify: 'simplify',
   adapt: 'simplify',
   // HARDEN - production-ready
-  normalize: 'harden',
   polish: 'harden',
   optimize: 'harden',
   harden: 'harden',
-  // SYSTEM - setup and tooling
-  extract: 'system',
 };
 
-export const CATEGORY_ORDER = ['create', 'evaluate', 'refine', 'simplify', 'harden', 'system'];
+export const CATEGORY_ORDER = ['create', 'evaluate', 'refine', 'simplify', 'harden'];
 
 export const CATEGORY_LABELS = {
   create: 'Create',