docs(spec): 订正 WidgetActionTypeSchema 的一处陈述 —— 派发源是 header action

#5010 退役 widget 级 actionType 后,「a type added to ActionType is
dispatchable from a widget」不再成立;唯一消费者是 DashboardHeaderActionSchema。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ehu85kbvMcrNTUJjwxvLJ9

Author: claude

packages/spec/src/ui/dashboard.zod.ts

@@ -51,8 +51,8 @@ export const WidgetColorVariantSchema = lazySchema(() => z.enum([
  * the shared dispatcher then executes at runtime.
  *
  * Derived rather than restated: a type added to `ActionType` is dispatchable
- * from a widget the moment the runner implements it, with no second list to
- * remember.
+ * from a header action the moment the runner implements it, with no second list
+ * to remember.
  */
 export const WidgetActionTypeSchema = lazySchema(() => ActionType.describe('Widget action type'));