feat(classes): session roster + manual waitlist promotion

Adds the roster and manual promotion controls deferred from the booking
lifecycle milestones. Businesses can now inspect who holds a seat and who
is queueing on a class session, and promote waitlisted customers by hand
— including a deliberate over-capacity override when the session is full.

Backend:
- GET /v1/catalog/class-sessions/{id}/roster — session metadata plus
  confirmed and waitlist entry lists with queue positions
- POST /v1/catalog/bookings/{id}/promote — 409 on a full session unless
  allowOverCapacity is set; 400 for non-waitlisted, 404 for missing or
  foreign bookings; reuses the shared confirm path so waitlist ledger
  rows resolve and reminder jobs re-arm
- ListBookingsBySession repository method (pgx + memory); ClassSession
  carries waitlistCount; UpcomingBooking carries classSessionId and
  waitlistPosition
- OpenAPI paths + schemas, regenerated client, catalog service tests

Frontend:
- classes tab session rows expand into a two-column roster panel with
  per-entry promote buttons and an explicit confirm-anyway step on 409
- booking detail modal shows waitlist position and offers promote for
  waitlisted bookings; list badges show #N queue positions
- CS/EN i18n keys and seeded demo roster data; demo mutations surface
  the demo notice

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

FRONTEND_ISSUES.md

@@ -39,3 +39,10 @@
 - Demo bootstrap slug aligned with backend demo tenant (`studio-atelier`).
 - Paddle mentions replaced by Stripe in legal + i18n copy.
 - `@neondatabase/neon-js` bumped to 0.7.0-beta — `npm audit` now reports 0 vulnerabilities.
+
+## Fixed This Session (class roster + waitlist promotion)
+
+- Class sessions in the zones classes tab now show a `N waiting` badge and expand into a two-column roster panel — confirmed attendees vs waitlist with `#N` queue positions, names, emails, and booking references.
+- Waitlisted roster entries have a **Confirm seat** action; when the session is full the backend returns 409 and the button re-arms into an explicit "confirm anyway" over-capacity step rather than silently overriding.
+- The booking detail modal now shows the waitlist position for waitlisted bookings and offers the same promote action (accent button above cancel); the bookings list badges waitlisted rows with their `#N` position.
+- Demo mode seeds a class session with a populated roster; mutation attempts surface the demo notice instead of failing. Verified in-browser in both Czech and English with a clean console.