docs: correct Wave 2 Task 7 Test-D description to the shipped move-under-area scenario

docs/plans/2026-06-06-playwright-coverage-fill-wave2.md

@@ -838,10 +838,15 @@ public async Task RenameArea_Escape_RevertsToOriginalLabel()
   `button.btn.btn-secondary.btn-sm:has-text('Close')`. `ShowDiff` computes the comparison
   centrally (no site relay), so it is deterministic for a deployed instance.
 
-**Step 1 — Test D: move a sub-area to the site root.** Create a parent area and a child area
-under it via CLI; in the UI, right-click the child → "Move to Area…" → pick "(Site root)" →
-Move; assert one toast; CLI read-back optional (the move toast + no error is sufficient;
-prefer asserting the area still exists). Cleanup deletes both areas in `finally`.
+**Step 1 — Test D: move one area under another area.** Create two root areas (parent, child)
+via CLI; in the UI, right-click the child → "Move to Area…" → select the **parent area** in
+the dialog → Move; assert one toast. (This exercises the reparenting path
+`_targetParentId = <non-null int>`, which is richer than the `null` site-root path; the move
+success toast fires only inside `SubmitMoveArea`'s `IsSuccess` branch, so toast-count-1 is
+itself persistence evidence — CLI read-back is optional and omitted.) Cleanup deletes the
+child then the parent in `finally` (child first, since after the move it is nested under the
+parent and the parent's delete would fail while it has a sub-area). Method name:
+`MoveArea_UnderAnotherArea_ShowsMovedToast`.
 
 ```csharp
 [SkippableFact]