Bump skills to 3.0, remove prefixed bundle, redesign install section

- Bump skills plugin version 2.1.1 -> 3.0.0 (plugin.json, marketplace.json,
  harness SKILL.md files). CLI and Chrome extension unchanged.
- Remove prefixed universal zip bundle and all related code:
  factory.js prefix/outputSuffix options, zip.js variant pass, utils.js
  prefixSkillReferences, the "universal-prefixed" entry in
  download-providers.js, and the matching test suite in utils.test.js.
- Redesign Get Started step 1 "Install the skill and CLI": two terminal
  rows (npx skills + npm i -g impeccable) with paired notes, drop the
  Recommended badge.
- Collapse "Other install methods" back into a <details> element so the
  primary install path is the first thing users see.
- Simplify step 3 to "Add the Chrome extension": remove the CLI tool
  block (now in step 1), use standard .btn .btn-primary for the CTA so
  it matches other primary buttons (square corners, accent slide-up
  hover), and lay out the preview screenshot next to the button instead
  of stacked so the screenshot no longer dominates vertical space.
- CLAUDE.md: rewrite with v3.0 architecture, the "no em dash also means
  no --" rule, the harness-dirs-are-tracked gotcha, the named-export
  test-spy warning, and the evals inline-skill.ts sync note.
- AGENTS.md, DEVELOP.md: drop prefixed variant references.

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

scripts/lib/utils.js

@@ -380,50 +380,14 @@ export const PROVIDER_PLACEHOLDERS = {
 /**
  * Replace all {{placeholder}} tokens with provider-specific values
  */
-/**
- * Prefix skill cross-references in body text.
- * Replaces patterns like `/skillname` and `the skillname skill` with prefixed versions.
- *
- * @param {string} content - The skill body text
- * @param {string} prefix - The prefix to add (e.g., 'i-')
- * @param {string[]} skillNames - Array of all skill names
- * @param {string} commandPrefix - The command invocation prefix (e.g., '/' or '$')
- */
-export function prefixSkillReferences(content, prefix, skillNames, commandPrefix = '/') {
-  if (!prefix || !skillNames || skillNames.length === 0) return content;
-
-  let result = content;
-  // Sort by length descending to avoid partial matches (e.g. 'teach-impeccable' before 'teach')
-  const sorted = [...skillNames].sort((a, b) => b.length - a.length);
-
-  for (const name of sorted) {
-    const prefixed = `${prefix}${name}`;
-
-    // Replace command invocations (e.g., `/skillname` or `$skillname`) with prefixed versions
-    const escapedPrefix = escapeRegex(commandPrefix);
-    result = result.replace(
-      new RegExp(`${escapedPrefix}(?=${escapeRegex(name)}(?:[^a-zA-Z0-9_-]|$))`, 'g'),
-      `${commandPrefix}${prefix}`
-    );
-
-    // Replace `the skillname skill` references
-    result = result.replace(
-      new RegExp(`(the) ${escapeRegex(name)} skill`, 'gi'),
-      (_, article) => `${article} ${prefixed} skill`
-    );
-  }
-
-  return result;
-}
-
 function escapeRegex(str) {
   return str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
 }
 
 const EXCLUDED_FROM_SUGGESTIONS = new Set([
-  'impeccable', 'i-impeccable',               // foundational skill, not a steering command
-  'teach-impeccable', 'i-teach-impeccable',    // deprecated shim
-  'frontend-design', 'i-frontend-design',      // deprecated shim
+  'impeccable',               // foundational skill, not a steering command
+  'teach-impeccable',         // deprecated shim
+  'frontend-design',          // deprecated shim
 ]);
 
 // Sub-commands of /impeccable that should appear in {{available_commands}}.