Check e.buttons to block hover events during any mouse-down drag

The isDraggingNodeRef check had a race condition: fast mouse movement
could trigger onMouseEnter before React Flow's onNodeDragStart fired.
Adding e.buttons !== 0 catches all cases where a button is held,
which is always true during drag, with no timing dependency.

https://claude.ai/code/session_01MvD1n4QeXutgwUpKJuDGHa

src/components/nodes/BaseNode.tsx

@@ -296,12 +296,12 @@ export function BaseNode({
           ${!fullBleed && selected && settingsExpanded ? "border-blue-500" : ""}
           ${className}
         `}
-        onMouseEnter={() => {
-          if (isPanningRef.current || isDraggingNodeRef.current) return;
+        onMouseEnter={(e) => {
+          if (e.buttons !== 0 || isPanningRef.current || isDraggingNodeRef.current) return;
           setHoveredNodeId(id);
         }}
-        onMouseLeave={() => {
-          if (isPanningRef.current || isDraggingNodeRef.current) return;
+        onMouseLeave={(e) => {
+          if (e.buttons !== 0 || isPanningRef.current || isDraggingNodeRef.current) return;
           setHoveredNodeId(null);
         }}
       >