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/styles.css

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