feat(10.1-02): render header and form partials through an allowlisted node renderer

- partialNodes rebuilds the server node tree with h() under the server's tag, attribute and URL lists
- PartialHost owns the skeleton, empty and failure states and keeps nodes visible on refetch
- type: partial is a valueless group-labelled field rendered on create and update
- ListView shows headerPartial above the list card and refetches it after bulk delete
- summer-partial and summer-stats style kit in main.css, documented in the cabana README; dist rebuilt

admin/tests/fixtures/extension.list-schema.json

@@ -0,0 +1,106 @@
+{
+  "data": {
+    "title": "Widgets",
+    "recordsPerPage": 20,
+    "perPageOptions": [],
+    "showSearch": true,
+    "showSetup": false,
+    "showCheckboxes": true,
+    "showSorting": true,
+    "searchTerm": "",
+    "recordUrl": "acme/demo/widgets/update/:id",
+    "toolbarButtons": [
+      "create",
+      "delete"
+    ],
+    "toolbarActions": [],
+    "assets": {
+      "scripts": [],
+      "styles": [
+        "/admin-test/assets/acme/demo/css/demo.css?v=abc"
+      ]
+    },
+    "columns": [
+      {
+        "key": "name",
+        "label": "Name",
+        "searchable": true,
+        "sortable": true
+      },
+      {
+        "key": "code",
+        "label": "Code",
+        "searchable": true,
+        "sortable": true
+      },
+      {
+        "key": "tags",
+        "label": "Tags",
+        "searchable": false,
+        "sortable": false,
+        "type": "relation",
+        "relation": "tags",
+        "select": "name"
+      },
+      {
+        "key": "created_at",
+        "label": "Created",
+        "searchable": false,
+        "sortable": true,
+        "type": "datetime"
+      },
+      {
+        "key": "active",
+        "label": "Active",
+        "searchable": false,
+        "sortable": false,
+        "type": "switch"
+      }
+    ],
+    "filters": [],
+    "rowActions": [],
+    "bulkActions": [],
+    "messages": {
+      "create": {
+        "other": "New widget"
+      },
+      "deleteConfirm": {
+        "one": "Delete :count widget?",
+        "other": "Delete :count widgets?"
+      },
+      "deleteSelected": {
+        "other": "Delete selected"
+      },
+      "deleted": {
+        "one": "Deleted :count widget",
+        "other": "Deleted :count widgets"
+      },
+      "empty": {
+        "other": "No widgets yet."
+      },
+      "emptySearch": {
+        "other": "Nothing found"
+      },
+      "emptySearchHint": {
+        "other": "No widget matches “:term”."
+      },
+      "recordCount": {
+        "one": ":count widget",
+        "other": ":count widgets"
+      },
+      "searchPrompt": {
+        "other": "Search widgets…"
+      },
+      "selected": {
+        "other": "Selected :count"
+      }
+    },
+    "meta": {
+      "locale": "en"
+    },
+    "headerPartial": "stats"
+  },
+  "meta": {
+    "locale": "en"
+  }
+}