refactor: import shared skills core in codex

.codex/superpowers-codex

@@ -4,6 +4,7 @@ const fs = require('fs');
 const path = require('path');
 const os = require('os');
 const { execSync } = require('child_process');
+const skillsCore = require('../lib/skills-core');
 
 // Paths
 const homeDir = os.homedir();