Restore confirmation modal for proceed with build button

chat/public/builder.js

@@ -113,8 +113,14 @@ async function proceedWithBuild(planContent) {
     el.modelSelectWrap.style.display = 'inline-flex';
   }
   
-  // Directly execute the build without showing confirmation modal
-  await executeBuild(planContent);
+  // Show confirmation modal before proceeding
+  if (el.confirmBuildModal) {
+    el.confirmBuildModal.style.display = 'flex';
+  } else {
+    // Fallback to confirm if modal not found for some reason
+    const confirmBuild = confirm("Are you sure you want to proceed with this plan? This will start the build process.");
+    if (confirmBuild) await executeBuild(planContent);
+  }
 }
 
 async function executeBuild(planContent) {