fix(reminders): re-arm reminder jobs on waitlist promotion

A booking promoted off the waitlist after its reminder had already
dispatched-as-skipped went unreminded. Promotion now clears pending
jobs and re-arms via the shared armReminderJobs helper — extracted
from booking creation so both paths arm email plus opt-in SMS.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

project.md

@@ -119,6 +119,7 @@
 - `[done/partial]` Milestone 18: Public class list polish
   - class sessions on the public booking page are now grouped by day (localized weekday + date headers) with compact timetable-style rows instead of one tall card per session — consistent with the stepped appointment picker above
   - capacity states read honestly: spots-left in success/warning tones, `Obsazeno`/`Full` when empty, and the action switches to `Na čekací listinu`/`Join waitlist` (previously a full session still said "Book now" while silently producing a waitlisted booking)
+  - reminder arming extracted into a shared `armReminderJobs` helper (email + opt-in SMS) used by booking creation and waitlist promotion — a booking promoted after its reminder already dispatched-as-skipped now gets re-armed instead of going unreminded
   - remaining: live staging validation
 
 ## Overview