Fix null crash from removed chat-agent-setup button

The gear button (chat-agent-setup) was removed from HTML but its
event listener in the renderer wasn't guarded with ?. — causing a
null reference that crashed init and prevented ALL subsequent event
handlers from registering (Folders, Wrap, JSON, Filter, etc.).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ozgesolidkey

src/renderer/renderer.ts

@@ -12907,7 +12907,7 @@ function init(): void {
   // Launch/Stop agent button
   elements.chatLaunchAgent.addEventListener('click', toggleAgent);
   // Agent setup wizard
-  elements.chatAgentSetup.addEventListener('click', async () => {
+  elements.chatAgentSetup?.addEventListener('click', async () => {
     const result = await showAgentWizard();
     if (result && !agentRunning) {
       const res = await window.api.launchAgent() as any;