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/src/api/schema.d.ts

@@ -1214,7 +1214,10 @@ export interface paths {
             path?: never;
             cookie?: never;
         };
-        /** Admin form schema */
+        /**
+         * Admin form schema
+         * @description The form of a controller, localized. `preview` is present when config_form.yaml declares a preview block: the form then has a read-only preview screen, which shows the fields whose context allows preview, the record actions and, when preview.headerPartial is set, that partial as a status hint.
+         */
         get: {
             parameters: {
                 query?: never;
@@ -4469,6 +4472,9 @@ export interface components {
             create: components["schemas"]["cabana.MessageForms"];
             deleteConfirm: components["schemas"]["cabana.MessageForms"];
             deleted: components["schemas"]["cabana.MessageForms"];
+            edit: components["schemas"]["cabana.MessageForms"];
+            /** @description The preview screen's subtitle and its edit button (D-11). */
+            preview: components["schemas"]["cabana.MessageForms"];
             saved: components["schemas"]["cabana.MessageForms"];
             update: components["schemas"]["cabana.MessageForms"];
         };
@@ -4479,6 +4485,9 @@ export interface components {
             label: string;
             value: components["schemas"]["cabana.jsonScalar"];
         };
+        "cabana.FormPreview": {
+            headerPartial?: string;
+        };
         "cabana.FormRedirect": {
             redirect: string;
             redirectClose: string;
@@ -4500,6 +4509,11 @@ export interface components {
             meta: components["schemas"]["cabana.FormMeta"];
             modelClass?: string;
             name?: string;
+            /**
+             * @description Preview is set when the form has a preview screen (D-11); a form
+             *     without one omits the key.
+             */
+            preview?: components["schemas"]["cabana.FormPreview"];
             /**
              * @description Redirects are the raw Winter config_form.yaml targets; the SPA maps
              *     them onto its routes.