feat: Week 2 improvements - coverage CI + command registry

Week 2 items from ARCHITECTURE-IMPROVEMENTS.md:

Item 4: Single source of truth ✅
- catalog.js already exists and works correctly
- All counts validated and passing

Item 5: Coverage metrics ✅
- Add c8 coverage reporting to CI (reusable-test.yml)
- Non-blocking with continue-on-error
- Upload coverage artifacts for visibility
- Existing npm run coverage script with 80% baseline

Item 6: Command → Agent/Skill map ✅
- New script: scripts/ci/generate-command-registry.js
- Scans commands/ for agent/skill references
- Outputs docs/COMMAND-REGISTRY.json
- NPM scripts: command-registry:generate, command-registry:write

🤖 Generated with [Claude Code](https://claude.com/claude-code)

package.json

@@ -285,6 +285,8 @@
     "postinstall": "echo '\\n  ecc-universal installed!\\n  Run: npx ecc typescript\\n  Compat: npx ecc-install typescript\\n  Docs: https://github.com/affaan-m/everything-claude-code\\n'",
     "catalog:check": "node scripts/ci/catalog.js --text",
     "catalog:sync": "node scripts/ci/catalog.js --write --text",
+    "command-registry:generate": "node scripts/ci/generate-command-registry.js",
+    "command-registry:write": "node scripts/ci/generate-command-registry.js --write",
     "lint": "eslint . && markdownlint '**/*.md' --ignore node_modules",
     "harness:adapters": "node scripts/harness-adapter-compliance.js",
     "harness:audit": "node scripts/harness-audit.js",