feat(10-02): backend strings, controller messages and declarative toolbar

- phrasebook ships the backend::lang admin strings (pl, en) with CLDR
  plural maps, loads them as namespace backend, applies
  pact.HasLangOverrides trees (lang/<locale>/<namespace>/<group>.yaml)
  after every namespace, and fails activation when a backend key cannot
  convert to plural forms
- Translator.Forms, Bundle, Resolved and Has serve keys as CLDR form maps
- Public GET /lang returns every backend::lang key for the request
  locale over the fallback locale, Cache-Control no-cache
- config_list, config_form and config_relation accept a strict messages
  block; omitted keys take framework defaults, schemas serve every message
  as CLDR forms, and activation fails on a missing phrase key
- toolbar.buttons is an ordered [create, delete] list; the Winter string
  form, duplicates, unknown actions and delete without showCheckboxes fail
  at boot, and create is dropped when the controller has no form
- Form schema serves the raw Winter redirects; scaffold emits the list
  syntax; form and relation schema routes are typed in the admin OpenAPI

cabana/form_schema.go

@@ -38,12 +38,13 @@ var (
 )
 
 type formConfigDocument struct {
-	Name            string         `yaml:"name"`
-	Form            string         `yaml:"form"`
-	ModelClass      string         `yaml:"modelClass"`
-	DefaultRedirect string         `yaml:"defaultRedirect"`
-	Create          *formRedirects `yaml:"create"`
-	Update          *formRedirects `yaml:"update"`
+	Name            string           `yaml:"name"`
+	Form            string           `yaml:"form"`
+	ModelClass      string           `yaml:"modelClass"`
+	DefaultRedirect string           `yaml:"defaultRedirect"`
+	Create          *formRedirects   `yaml:"create"`
+	Update          *formRedirects   `yaml:"update"`
+	Messages        *formMessageKeys `yaml:"messages"`
 }
 
 type formRedirects struct {
@@ -102,11 +103,22 @@ func CompileForm(pluginID string, ctl pact.AdminController, fsys fs.FS) (*FormSc
 	if err := requireDropdownProvider(ctl, fields); err != nil {
 		return nil, bootErr(pluginID, ctl.ID(), fieldsPath, err)
 	}
-	return &FormSchema{
+	schema := &FormSchema{
 		Name:       doc.Name,
 		ModelClass: doc.ModelClass,
 		Fields:     fields,
-	}, nil
+		redirects:  FormRedirects{Default: doc.DefaultRedirect},
+	}
+	if doc.Messages != nil {
+		schema.messageKeys = *doc.Messages
+	}
+	if doc.Create != nil {
+		schema.redirects.Create = FormRedirect{Redirect: doc.Create.Redirect, RedirectClose: doc.Create.RedirectClose}
+	}
+	if doc.Update != nil {
+		schema.redirects.Update = FormRedirect{Redirect: doc.Update.Redirect, RedirectClose: doc.Update.RedirectClose}
+	}
+	return schema, nil
 }
 
 // Localize copies the cached schema and resolves display strings for one request.
@@ -141,6 +153,8 @@ func (s *FormSchema) Localize(ctx context.Context, tr *phrasebook.Translator, pr
 		Name:       translateKey(ctx, tr, s.Name),
 		ModelClass: s.ModelClass,
 		Fields:     fields,
+		Messages:   localizeMessages[formMessageKeys, FormMessages](ctx, tr, s.formMessageKeySet()),
+		Redirects:  s.redirects,
 		Meta:       FormMeta{Locale: locale},
 	}, nil
 }