Trim changelog to user-facing changes only

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

public/index.html

@@ -307,10 +307,7 @@
           <ul class="changelog-items">
             <li>Added Kiro support (<code>.kiro/skills/</code>)</li>
             <li>Restored prefix toggle — download <code>i-</code> prefixed bundles to avoid naming conflicts</li>
-            <li>Skills now prefix all cross-references when using prefixed bundles</li>
             <li>Audit and critique skills only suggest real, installed commands</li>
-            <li>Security hardening: input validation, error sanitization, security headers</li>
-            <li>Simplified build output to universal ZIPs only</li>
           </ul>
         </div>