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;
 }
 

server/src/wled_controller/static/js/core/graph-nodes.js

@@ -346,6 +346,14 @@ function _createOverlay(node, nodeWidth, callbacks) {
         width: totalW, height: btnSize + 4,
     }));
 
+    const ACTION_LABELS = {
+        startstop: node.running ? 'Stop' : 'Start',
+        test: 'Test / Preview',
+        notify: 'Test notification',
+        edit: 'Edit',
+        delete: 'Delete',
+    };
+
     btns.forEach((btn, i) => {
         const bx = ox + 4 + i * (btnSize + btnGap);
         const by = oy + 2;
@@ -354,6 +362,9 @@ function _createOverlay(node, nodeWidth, callbacks) {
         const txt = svgEl('text', { x: bx + btnSize / 2, y: by + btnSize / 2 });
         txt.textContent = btn.icon;
         bg.appendChild(txt);
+        const btnTip = svgEl('title');
+        btnTip.textContent = ACTION_LABELS[btn.action] || btn.action;
+        bg.appendChild(btnTip);
         bg.addEventListener('click', (e) => {
             e.stopPropagation();
             if (btn.action === 'edit' && callbacks.onEditNode) callbacks.onEditNode(node);