fix: constrain loading overlays to components

- Add position: relative to create-session-form-wrapper so overlay fills only the form
- Remove text from instance busy overlay, show only spinner
- Delete progress indicator now fills only the target card

apps/web/src/components/instance-list.tsx

@@ -224,7 +224,6 @@ export const InstanceList = ({ projectId, repoId, projectName, repoName, toolTyp
               {busyInstanceId === instance.id && (
                 <div className="instance-busy-overlay">
                   <Icon name="loading" size="md" />
-                  <span>Working...</span>
                 </div>
               )}
               <div className="instance-info">

apps/web/src/styles.css

@@ -2885,6 +2885,10 @@ a.nav-item,
   pointer-events: none;
 }
 
+.create-session-form-wrapper {
+  position: relative;
+}
+
 .loading-overlay {
   position: absolute;
   top: 0;