feat(reminders): SMS channel for reminder jobs

Tenants paying for the SMS add-on still got email-only reminders —
the channel column existed but nothing armed or dispatched sms jobs.
Booking creation now adds a second job when SMS is enabled and the
customer left a phone; dispatch routes sms jobs through an injected
sender adapter wired to the existing sms.Service, so monthly limits,
usage metering, and Stripe billing apply unchanged. Lifecycle handling
from the previous milestone clears and re-arms both channels together.

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project.md

@@ -101,6 +101,12 @@
   - KPI grid rebalanced for five cards (`lg:grid-cols-3 xl:grid-cols-5`); `new_clients` maps to the existing `dashboard.kpi.newClients` i18n key
   - reminder dispatch now has a real trigger: `.github/workflows/reminder-dispatch.yml` calls `POST /v1/internal/jobs/reminders/dispatch` every 15 minutes with `X-Bookra-Job-Key` from secrets (`BOOKRA_API_URL`, `BOOKRA_JOB_RUNNER_KEY`); jobs are timestamp-based so scheduler lateness delays but never skips
   - remaining: live staging validation; the workflow no-ops gracefully until the two secrets are configured
+- `[done/partial]` Milestone 15: SMS reminder channel
+  - booking creation arms a second reminder job on `channel: sms` when the tenant has SMS enabled (`tenant_sms_settings.enabled`) and the customer left a phone number; email jobs are unchanged
+  - `notifications.Service` gained an injected `smsSender` function adapter (wired to `sms.Service.SendMessage` in the API server, keeping the package dependency-free); dispatch routes `channel: sms` through it with localized body text and the customer phone as recipient
+  - `sms.Service.SendMessage` still enforces enabled/plan/monthly-limit and logs usage, so SMS reminders inherit metering and billing automatically; missing provider config or phone marks the job `failed` with a delivery-log reason
+  - reminder lifecycle work from milestone 13 applies per-booking, so cancel/reschedule clears and re-arms both channels
+  - remaining: live staging validation against a real SMS Manager key
 
 ## Overview
 Bookra is a Czech-first booking SaaS for small local service businesses. It targets salons, massage therapists, small clinics, repair shops, and small studios/clubs that need a simple public booking flow, internal schedule management, reminders, and basic business reporting without becoming a full ERP.