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- Add `staffReadAt` column to conversations table schema - Add migration 0032_staff_read_at.sql for the new column - Create /api/conversations router with GET / (list), GET /:id/messages (paginated), POST /:id/messages (send) - Mark conversations as read (staffReadAt = NOW()) when staff fetches messages - Return 409 when client has opted out of SMS - 404 on cross-tenant access - Add conversations.test.ts covering all 5 acceptance criteria Co-Authored-By: Paperclip <noreply@paperclip.ing>