feat(p9): thread purpose + persist consent receipt through OutboundService

Task S2.2: OutboundService.send gains an optional purpose, passes it to the broker,
and persists the returned consentReceiptRef on IiosOutboundCommand (new nullable
column, migration outbound-consent). RouteService.execute passes 'route_forward';
calendar reminders pass 'meeting_reminder'. CMP-DENY → command BLOCKED, no send.
2 tests: receipt recorded on allow, purpose-DENY blocks.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/src/calendar/calendar.service.ts

@@ -178,6 +178,8 @@ export class CalendarService {
       `meeting:${meeting.id}`,
       { text: `Reminder: "${meeting.title}"` },
       `meeting-reminder:${meeting.id}`,
+      meeting.scopeId,
+      'meeting_reminder',
     );
     for (const p of meeting.participants) {
       if (!p.actorRefId) continue;