feat(12.2-03): add hasMany relation contracts, relation forms and child create

- RelationContract gains Kind (empty is belongsToMany) and ForeignKey, with kind-aware boot checks
- manage.form, view.form and pivot.form compile against the related or pivot model; $/ paths resolve inside the plugin
- view toolbarButtons accept create|update|delete|link|unlink, each the capability of its routes
- POST .../relations/{name}/records creates a child through the manage form; the server sets the hasMany key
- relation schema carries kind, deferrable and the localized forms; 17 new relation message keys in en and pl

modules/cabana/http.go

@@ -275,6 +275,10 @@ func (s *service) mount(r pact.Router) {
 		constrainRelation(g)
 		g.Post("/{vendor}/{plugin}/{controller}/{id}/relations/{name}/unlink", requireAjax(s.relationUnlink))
 		constrainRelation(g)
+		// Relation child routes (D-11, D-12): create through the relation's
+		// manage form.
+		g.Post("/{vendor}/{plugin}/{controller}/{id}/relations/{name}/records", requireAjax(s.relationChildCreate))
+		constrainRelation(g)
 		// File routes of `type: fileupload` fields (D-09). {id} 0 is the
 		// record being created in the X-Session-Key session.
 		g.Post("/{vendor}/{plugin}/{controller}/{id}/files/{field}", requireAjax(s.fileUpload))
@@ -577,7 +581,7 @@ func (s *service) relations() (RelationService, error) {
 	if err != nil {
 		return RelationService{}, err
 	}
-	return RelationService{DB: db}, nil
+	return RelationService{DB: db, bucket: s.bucket(), tr: s.translator()}, nil
 }
 
 func (s *service) formSchema(w http.ResponseWriter, r *http.Request) {