fix: use ReadonlySet<string> for TARGET_REQUIRED_TYPES to fix DTS build error

The Set narrowed type Exclude<ActionType, 'script'> was incompatible with
Set.has() receiving the full ActionType union in strict TypeScript DTS emit.

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

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

@@ -28,8 +28,8 @@ export const ActionType = z.enum(['script', 'url', 'modal', 'flow', 'api']);
  * These types reference an external resource (URL, flow, modal, or API endpoint)
  * and cannot function without a target binding.
  */
-const TARGET_REQUIRED_TYPES = new Set(
-  ActionType.options.filter((t): t is Exclude<typeof t, 'script'> => t !== 'script'),
+const TARGET_REQUIRED_TYPES: ReadonlySet<string> = new Set(
+  ActionType.options.filter((t) => t !== 'script'),
 );
 
 /**