Adopt shared WebUI structural primitives

docs/INTERFACE_PATTERN_MIGRATION.md

@@ -31,9 +31,14 @@ through declared capabilities or metadata.
 
 ## Interaction evidence
 
-- `AdminPageLayout`, `TreeSubnav`, `DataGrid`, `Dialog`, `ConfirmDialog`,
+- `WorkspaceLayout`, headerless `PageLayout`, `AdminPageLayout`, `TreeSubnav`,
+  `DataGrid`, `Dialog`, `ConfirmDialog`,
   `TableActionGroup`, `PasswordField`, `ActionBlockerHint`, and
   `DocumentationHelpLink` come from Core.
+- The administration tree and its contributed panels now share Core-owned pane
+  sizing, scrolling, content inset, responsive collapse, region labels, and
+  contextual-help identity; Access no longer carries a raw workspace or page
+  frame exception.
 - Dialog focus trapping and restoration, disabled-action tooltips, keyboard
   ordering, responsive grid overflow, and alert semantics therefore inherit
   the tested Core behavior.