feat(12.1-02): read-only preview screen with a status hint and record actions

- config_form.yaml preview block (optional headerPartial), reported in the form schema as preview
- fields with context: preview show only on the preview screen and are never written
- form messages preview and edit; recordActions without a preview block stops boot
- SPA route {id}/preview, PreviewView and PreviewField, record actions in the footer
- mapWinterUrl maps preview/:id; the update form returns to the preview
- summer-callout partial style classes for status hints
- README, docs, OpenAPI document, TS types and the embedded build updated

admin/tests/smoke/edit.smoke.test.ts

@@ -68,7 +68,8 @@ describe('winter URLs', () => {
     expect(mapWinterUrl('/acme/demo/widgets/create', id)).toBe('/acme/demo/widgets/create')
     expect(mapWinterUrl('acme/demo/widgets/update/:id', id, 42)).toBe('/acme/demo/widgets/42')
     expect(mapWinterUrl('acme/demo/widgets/update/:id', id, null)).toBe('/acme/demo/widgets')
-    expect(mapWinterUrl('acme/demo/widgets/preview/:id', id, 42)).toBe('/acme/demo/widgets')
+    expect(mapWinterUrl('acme/demo/widgets/preview/:id', id, 42)).toBe('/acme/demo/widgets/42/preview')
+    expect(mapWinterUrl('acme/demo/widgets/history/:id', id, 42)).toBe('/acme/demo/widgets')
     expect(mapWinterUrl('https://evil.example/acme/demo/widgets', id, 1)).toBe('/acme/demo/widgets')
     expect(mapWinterUrl('acme/other/things/update/:id', id, 1)).toBe('/acme/demo/widgets')
     expect(mapWinterUrl('', id)).toBe('/acme/demo/widgets')