Add booking stack, client deploys, and back-office updates

- deploy/booking: shared Easy!Appointments stack with brand-matched
  wizard (flatpickr recolor, single-tenant provider hide, iframe
  auto-fit height reporter)
- deploy/clients: per-client isolated nginx compose stacks with
  _template scaffold, new-client.sh, and happynails live site
- deploy/backup: smb-db backup script
- n8n: booking-sync workflow; onboarding tweaks
- playbooks: lead-to-customer lifecycle + outreach
- templates: nail-studio landing previews
- backoffice: app/db/init/compose updates

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backoffice/db/init.sql

@@ -21,6 +21,7 @@ CREATE TABLE IF NOT EXISTS clients (
     renewal_date     date,
     created_at       timestamptz,
     notes            text,
+    notify_channel   text,
     updated_at       timestamptz NOT NULL DEFAULT now()
 );