- Add TicketComment model for conversation threads (append-only)
- Add paymentInstructions field to TenantSettings
- Add ticketComments relation to User model
- Create portal-ticket-service with ensurePortalUser shadow User pattern
- Implements createPortalTicket, listPortalTickets, getPortalTicket, addTicketComment
- Portal ticket creation delegates to existing createTicket with source=SUBSCRIBER
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>