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>
