Add per-button tooltips to graph overlay and widen stream test modal

- Each graph node overlay button now has its own <title> tooltip
  (Edit, Delete, Start/Stop, Test, etc.) instead of inheriting the
  card name from the parent group
- Widen #test-stream-modal to 700px (matching CSS source test modal)

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

server/src/wled_controller/static/css/modal.css

@@ -346,7 +346,8 @@
     margin: 0 4px;
 }
 
-#test-css-source-modal .modal-content {
+#test-css-source-modal .modal-content,
+#test-stream-modal .modal-content {
     max-width: 700px;
 }