chore(release): 4.6.0 - SPDD & Radix UI Design System

- Bump version to 4.6.0, update CHANGELOG and README counts to 626
- Fix listSkillIds to only include dirs with SKILL.md (SPDD excluded from catalog)
- Regenerate catalog and index after PR 47/48 merge

lib/skill-utils.js

@@ -149,7 +149,13 @@ function readSkill(skillDir, skillId) {
 
 function listSkillIds(skillsDir) {
   return fs.readdirSync(skillsDir)
-    .filter(entry => !entry.startsWith('.') && fs.statSync(path.join(skillsDir, entry)).isDirectory())
+    .filter(entry => {
+      if (entry.startsWith('.')) return false;
+      const dirPath = path.join(skillsDir, entry);
+      if (!fs.statSync(dirPath).isDirectory()) return false;
+      const skillPath = path.join(dirPath, 'SKILL.md');
+      return fs.existsSync(skillPath);
+    })
     .sort();
 }