fix(11-05): CR-01 surface reminderIsCustom to preserve custom VALARMs on edit

- expand.ts: add reminderIsCustom:boolean to CalendarOccurrence interface;
  derived from classifyValarms kind==='custom'; propagated to both
  non-recurring and recurring occurrence branches
- client.ts: mirror reminderIsCustom on CalendarOccurrence (atomic mirror)
- EventForm.tsx: extend deriveReminderValue to accept isCustom flag;
  returns '__custom__' when true, making the existing D-08 preserve branch
  live — editing a custom-alarm event now omits reminderLeadMinutes from
  the payload so outboxWorker extractValarms keeps the original VALARM
- Fix existing test fixtures (EventForm.test.tsx, EventDetailPopover.test.tsx)
  to include reminderIsCustom:false on all CalendarOccurrence literals

Fixes CAL-14 Pitfall 1: Apple Calendar absolute DATE-TIME / multi-VALARM
alarms no longer silently stripped on any edit round-trip from the PWA.

apps/api/src/broker/expand.ts

@@ -80,6 +80,13 @@ export interface CalendarOccurrence {
    *   positive — N minutes before event start (timed) or N/1440 days before (all-day)
    */
   reminderLeadMinutes: number | null;
+  /**
+   * True when the master event's alarm is a custom/absolute/multi-VALARM not reducible
+   * to a single before-event lead (CAL-14, CR-01, Phase 11 Plan 05).
+   * When true, reminderLeadMinutes is always null and the edit form must initialize the
+   * picker to '__custom__' to emit an absent payload field and preserve the original VALARM.
+   */
+  reminderIsCustom: boolean;
 }
 
 /**
@@ -241,9 +248,14 @@ export function expandOccurrences(
   // event's VALARM via classifyValarms. All occurrences inherit this value (series-level, D-10).
   // preset/offlist → specific leadMinutes; custom/none → null (D-07/NOTIF-05).
   // classifyValarms wraps ICAL.parse in try/catch (T-11-07 safe); safe on parse failure → null.
+  //
+  // Phase 11 Plan 05 (CR-01): reminderIsCustom — surface the 'custom' classification so the
+  // edit form can initialize the picker to '__custom__' and emit an absent payload field,
+  // preserving the original VALARM via the outboxWorker D-08 preserve path.
   const alarmClass = classifyValarms(rawVevent);
   const reminderLeadMinutes: number | null =
     alarmClass.kind === 'preset' || alarmClass.kind === 'offlist' ? alarmClass.leadMinutes : null;
+  const reminderIsCustom: boolean = alarmClass.kind === 'custom';
 
   // --- 4. Non-recurring event: single occurrence check ---
   if (!isRecurring) {
@@ -281,6 +293,7 @@ export function expandOccurrences(
         description: event.description ?? null,
         hasRrule: isRecurring, // always false in the non-recurring branch
         reminderLeadMinutes, // series-level (D-10)
+        reminderIsCustom, // CR-01 (Plan 05): true when alarm is absolute/multi-VALARM
       });
     }
     return occurrences;
@@ -329,6 +342,7 @@ export function expandOccurrences(
       description: event.description ?? null,
       hasRrule: isRecurring, // always true in the recurring branch
       reminderLeadMinutes, // series-level — all occurrences inherit the master's value (D-10)
+      reminderIsCustom, // CR-01 (Plan 05): true when alarm is absolute/multi-VALARM
     });
   }