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

modules/cabana/testdata/roster/controllers/people/_status.htm

@@ -0,0 +1,6 @@
+{{- if .Data.Title -}}
+<div class="summer-callout summer-callout--{{ .Data.Tone }}" role="status">
+<p class="summer-callout__title">{{ trans .Data.Title }}</p>
+<p class="summer-callout__text">{{ trans .Data.Text }}</p>
+</div>
+{{- end -}}