feat(web): add workflow graph editor and try-mode JSON tree

Add a Graph tab (React Flow) as the default workflow editor view, drop the Mermaid YAML preview, auto-assign step-N ids on add, and show test results as a JSON tree.

Co-authored-by: Nasyarobby Putra <nasyarobby@gmail.com>

packages/web/src/index.css

@@ -25,6 +25,7 @@ body,
   transition: transform 0.7s ease-out;
 }
 
-.mermaid-clickable [id^="s"] {
-  cursor: pointer;
+.workflow-graph {
+  width: 100%;
+  height: 100%;
 }