feat(11-04): add reminderLeadMinutes to CreateEventPayload + CalendarOccurrence

- CalendarOccurrence: required reminderLeadMinutes: number | null (atomic mirror of expand.ts, Plan 11-03)
- CreateEventPayload: optional reminderLeadMinutes?: number | null with absent/null/0/positive contract (D-08)
- Update CalendarOccurrence fixtures in EventForm.test.tsx + EventDetailPopover.test.tsx to include the new required field (reminderLeadMinutes: null)
- pwa tsc --noEmit exits 0

apps/pwa/src/api/client.ts

@@ -131,6 +131,14 @@ export interface CalendarOccurrence {
    * stay in sync with the server type (Pitfall 4 — atomic mirror, Plan 06-05).
    */
   hasRrule: boolean;
+  /**
+   * Per-event reminder lead in minutes. NULL = no reminder. 0 = same-day all-day
+   * (fire 9 AM on event date). Positive integer = N minutes before event start.
+   * D-06: NULL and 0 are semantically distinct.
+   * Mirrors CalendarOccurrence.reminderLeadMinutes in apps/api/src/broker/expand.ts
+   * (atomic mirror, Plan 11-03).
+   */
+  reminderLeadMinutes: number | null;
 }
 
 export interface OccurrencesResponse {
@@ -194,6 +202,14 @@ export interface CreateEventPayload {
   recurrenceCount?: number;
   location?: string;
   description?: string;
+  /**
+   * Per-event reminder lead in minutes.
+   * absent/undefined = no-change (edit omits field so server preserves existing VALARM, D-08)
+   * null             = explicit "None" (clear any VALARM)
+   * 0                = same-day all-day (fire 9 AM on event date, D-05)
+   * positive integer = N minutes before event start
+   */
+  reminderLeadMinutes?: number | null;
   calendarUrl?: string; // omit to use the member's default writable calendar (D-01)
 }