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/openapi/admin.json

@@ -846,6 +846,17 @@
                     "deleted": {
                         "$ref": "#/components/schemas/cabana.MessageForms"
                     },
+                    "edit": {
+                        "$ref": "#/components/schemas/cabana.MessageForms"
+                    },
+                    "preview": {
+                        "allOf": [
+                            {
+                                "$ref": "#/components/schemas/cabana.MessageForms"
+                            }
+                        ],
+                        "description": "The preview screen's subtitle and its edit button (D-11)."
+                    },
                     "saved": {
                         "$ref": "#/components/schemas/cabana.MessageForms"
                     },
@@ -857,6 +868,8 @@
                     "create",
                     "deleteConfirm",
                     "deleted",
+                    "edit",
+                    "preview",
                     "saved",
                     "update"
                 ],
@@ -888,6 +901,14 @@
                 ],
                 "type": "object"
             },
+            "cabana.FormPreview": {
+                "properties": {
+                    "headerPartial": {
+                        "type": "string"
+                    }
+                },
+                "type": "object"
+            },
             "cabana.FormRedirect": {
                 "properties": {
                     "redirect": {
@@ -955,6 +976,14 @@
                     "name": {
                         "type": "string"
                     },
+                    "preview": {
+                        "allOf": [
+                            {
+                                "$ref": "#/components/schemas/cabana.FormPreview"
+                            }
+                        ],
+                        "description": "Preview is set when the form has a preview screen (D-11); a form\nwithout one omits the key."
+                    },
                     "redirects": {
                         "allOf": [
                             {
@@ -3262,6 +3291,7 @@
         },
         "/{vendor}/{plugin}/{controller}/schema/form": {
             "get": {
+                "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.",
                 "parameters": [
                     {
                         "description": "Vendor",