FN-6079: fix mobile workflow editor edge rendering

Ensure the mobile workflow editor keeps the React Flow surface tall enough for edges to render correctly.

- add a full-height mobile rule for the workflow editor React Flow surface
- extend the mobile CSS contract test to assert the height requirement
- broaden the selector width test to cover the collapsed workflow selector button

Files changed:
 packages/dashboard/app/components/WorkflowNodeEditor.css            | 1 +
 .../app/components/__tests__/WorkflowNodeEditor.css.test.ts         | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

Fusion-Task-Id: FN-6079

Fusion-Task-Lineage: a6f1de35-ce99-4673-bfaf-183124969a7c

packages/dashboard/app/components/WorkflowNodeEditor.css

@@ -1334,6 +1334,7 @@
     width: 100%;
     min-width: 0;
     max-width: 100%;
+    height: 100%;
   }
 
   .wf-editor-list-item,