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/messages.go

@@ -68,6 +68,9 @@ type formMessageKeys struct {
 	Saved         string `yaml:"saved"`
 	DeleteConfirm string `yaml:"deleteConfirm"`
 	Deleted       string `yaml:"deleted"`
+	// The preview screen's subtitle and its edit button (D-11).
+	Preview string `yaml:"preview"`
+	Edit    string `yaml:"edit"`
 }
 
 // FormMessages is a form's copy, every key resolved.
@@ -77,6 +80,9 @@ type FormMessages struct {
 	Saved         MessageForms `json:"saved"`
 	DeleteConfirm MessageForms `json:"deleteConfirm"`
 	Deleted       MessageForms `json:"deleted"`
+	// The preview screen's subtitle and its edit button (D-11).
+	Preview MessageForms `json:"preview"`
+	Edit    MessageForms `json:"edit"`
 }
 
 // relationMessageKeys is one config_relation.yaml relation's messages block.
@@ -162,6 +168,8 @@ var (
 		Saved:         "backend::lang.messages.form.saved",
 		DeleteConfirm: "backend::lang.messages.form.delete_confirm",
 		Deleted:       "backend::lang.messages.form.deleted",
+		Preview:       "backend::lang.messages.form.preview",
+		Edit:          "backend::lang.messages.form.edit",
 	}
 	relationMessageDefaults = relationMessageKeys{
 		Link:             "backend::lang.messages.relation.link",