feat(12.1-01): declared bulk actions on admin lists

- pact.HasAdminBulkActions with AdminBulkAction, its input and result
- config_list.yaml bulkActions, compiled fail-loud, needs showCheckboxes
- POST .../{controller}/bulk/{action}: ids resolved and locked through the
  list scope in one transaction; partial selection is 409
- list schema offers declared actions per principal, with confirm text
- admin SPA bulk actions menu with confirm, busy state and failure toasts
- acme.roster fixture, tracer test, OpenAPI, TS types, dist, READMEs, docs

modules/cabana/contracts.go

@@ -79,6 +79,10 @@ type CompiledController struct {
 	// the single namespace that toolbar.buttons names and widget action: keys
 	// resolve through. create and delete are reserved built-in names.
 	Actions map[string]pact.AdminAction
+	// BulkActions are the controller's pact.HasAdminBulkActions entries keyed
+	// by name. They have their own namespace next to Actions; create and
+	// delete are reserved there too.
+	BulkActions map[string]pact.AdminBulkAction
 
 	// scripts and styles are the controller's declared plugin JS and CSS,
 	// in declared order.