Docs: preview start_date defaults to the household-local today

The occurrence-preview request docstring and the admin client's
startDate comment still said the default is the API host's today. The
route defaults to the household-local today in the configured
timezone, and uses the host's local time only when that setting is empty.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

admin/src/api/definitions.ts

@@ -150,7 +150,10 @@ export async function updateDefinition(
 export const OCCURRENCES_PREVIEW_PATH = `${DEFINITIONS_PATH}/occurrences-preview`;
 
 export interface OccurrencesPreviewOptions {
-  /** "YYYY-MM-DD"; the API defaults to its host's today. */
+  /**
+   * "YYYY-MM-DD"; the API defaults to the household-local today in the
+   * configured `timezone` (the API host's local time when that is empty).
+   */
   startDate?: string;
   /** 1..50; the API defaults to 10. */
   count?: number;