fix(plugin): slim Claude Code install (291MB→770KB) + fix skills path

- Marketplace source moved from "./" to "./plugin", a thin generated
  subtree containing only the plugin manifest and the impeccable skill.
  Per-version plugin cache shrinks ~378× (~770 KB instead of ~291 MB),
  and the lockfile is no longer included in the source path so the
  cache extraction never runs bun install. (#107)
- skills field in plugin.json now ends with a trailing slash to match
  the documented schema (code.claude.com/docs/en/plugins-reference,
  every directory example uses ./path/). Three reporters converged on
  this fix because Claude Code's plugin loader skips command
  registration on some setups when the slash is missing. (#86)
- Anti-patterns maintenance agent moved out of .claude/agents/ into
  CLAUDE.md / AGENTS.md as concise inline guidance, since it is
  repo-internal dev workflow, not user-facing. The plugin was also
  the only place this agent was exposed to install users.
- Skills version bumped to 3.0.2 so existing users pick up the new
  install path on next /plugin update.
- Top-level harness directories (.claude/skills/, .cursor/skills/, ...)
  intentionally stay where they are; npx skills add reads them
  directly from the GitHub repo and that path is unaffected.

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

scripts/build.js

@@ -672,6 +672,37 @@ async function build() {
 
   console.log(`📋 Synced skills to: ${syncConfigs.map(p => p.configDir).join(', ')}`);
 
+  // Build the Claude Code plugin subtree at ./plugin/.
+  // The Claude Code marketplace is configured with `source: "./plugin"`, so
+  // the plugin cache only copies this slim directory (~0.3 MB) instead of
+  // the entire monorepo (~291 MB on the previous "./" source). The harness
+  // dirs above stay where they are because `npx skills add pbakaus/impeccable`
+  // reads them directly from the GitHub repo at install time.
+  const pluginRoot = path.join(ROOT_DIR, 'plugin');
+  const pluginManifestDir = path.join(pluginRoot, '.claude-plugin');
+  const pluginSkillsDir = path.join(pluginRoot, 'skills');
+  if (fs.existsSync(pluginManifestDir)) fs.rmSync(pluginManifestDir, { recursive: true });
+  if (fs.existsSync(pluginSkillsDir)) fs.rmSync(pluginSkillsDir, { recursive: true });
+
+  const rootManifest = JSON.parse(fs.readFileSync(path.join(ROOT_DIR, '.claude-plugin/plugin.json'), 'utf-8'));
+  // Trailing slash on the skills path matches the documented schema in
+  // code.claude.com/docs/en/plugins-reference. Issue #86 has 3 reporters
+  // converging on "add trailing slash to fix slash commands not registering";
+  // the docs schema example consistently uses `"./custom/skills/"` form.
+  const pluginManifest = { ...rootManifest, skills: './skills/' };
+  fs.mkdirSync(pluginManifestDir, { recursive: true });
+  fs.writeFileSync(
+    path.join(pluginManifestDir, 'plugin.json'),
+    JSON.stringify(pluginManifest, null, 2) + '\n',
+  );
+
+  const claudeSkillsSrc = path.join(DIST_DIR, 'claude-code', '.claude', 'skills', 'impeccable');
+  if (fs.existsSync(claudeSkillsSrc)) {
+    fs.mkdirSync(pluginSkillsDir, { recursive: true });
+    copyDirSync(claudeSkillsSrc, path.join(pluginSkillsDir, 'impeccable'));
+  }
+
+  console.log('📦 Built Claude Code plugin subtree at ./plugin/');
 
   // Generate authoritative counts and validate references
   const countErrors = generateCounts(ROOT_DIR, skills, buildDir);