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/phase10_csrf_test.go

@@ -68,9 +68,9 @@ func TestPhase10CSRF(t *testing.T) {
 	}
 	// refresh, logout, settings put, create, bulk-delete, widget action,
 	// toolbar action, update, delete, link, unlink, file upload, file
-	// reorder, file caption, file remove
-	if unsafe != 15 {
-		t.Fatalf("walked %d state-changing routes, want 15: %v", unsafe, router.order)
+	// reorder, file caption, file remove, relation child create
+	if unsafe != 16 {
+		t.Fatalf("walked %d state-changing routes, want 16: %v", unsafe, router.order)
 	}
 
 	loginHandler := router.handlers[login]