feat(ui): add ActionItem.reminder_set to the TS type (T8.6, FR-CAL-5)

src/lib/api.ts

@@ -110,6 +110,8 @@ export interface ActionItem {
   owner: string | null;
   due_at: number | null;
   confirmed: boolean;
+  // Schedule a local OS reminder for due_at (Phase 8, T8.6, FR-CAL-5).
+  reminder_set: boolean;
 }
 
 // On-disk shape of summary.json (FR-LLM-2/4) — `null` until generate_summary