feat(scheduling): dezky Scheduling — Calendly-style booking on Stalwart calendars

First-party booking system on top of Stalwart calendars (no third-party
scheduling dependency). Hosts expose public booking pages; visitors pick a
slot computed from the host's live Stalwart free/busy, and confirming writes
the event to the host's calendar and sends a dezky-branded confirmation with
an .ics.

platform-api (services/platform-api/src/scheduling):
- Schemas: Host, StalwartCredential (AES-256-GCM at rest), AvailabilitySchedule,
  EventType, Booking, SlotLock (unique (hostId,startUtc) + TTL).
- StalwartCalendarModule: JMAP gateway (free/busy via Principal/getAvailability,
  event create/delete, scheduleAgent=client) + on-behalf app-password
  provisioning. CredentialCipher for at-rest encryption.
- DST-correct slot engine (Luxon) with unit tests; two-layer double-booking
  guard (atomic SlotLock + live free/busy re-check).
- Booking confirm/cancel/reschedule, branded email + .ics via JMAP submission,
  self-service manage tokens. /api/v1 public + tenant-gated admin routes,
  per-IP rate limiting.

apps/booking: standalone public, whitelabel booking app (booking.dezky.eu) —
path-based tenant resolution, per-tenant brand colour, booking + manage flows.

apps/portal: admin scheduling page (hosts, event types, availability, bookings
with edit/delete + admin cancel/reschedule) and proxy routes.

infra: booking dev service in docker-compose; scheduling env vars.

apps/booking/Dockerfile

@@ -0,0 +1,22 @@
+# Production image for the dezky booking app (Nuxt 4 SSR).
+# Build context = this directory (apps/booking).
+# syntax=docker/dockerfile:1
+
+FROM node:22-alpine AS build
+WORKDIR /app
+RUN corepack enable
+COPY package.json pnpm-lock.yaml ./
+RUN pnpm install --frozen-lockfile
+COPY . .
+RUN pnpm build
+
+FROM node:22-alpine AS runtime
+WORKDIR /app
+ENV NODE_ENV=production
+ENV HOST=0.0.0.0
+ENV PORT=3000
+ENV NUXT_PUBLIC_SITE_URL=https://booking.dezky.eu
+# Set PLATFORM_API_INTERNAL_URL at deploy time to reach platform-api.
+COPY --from=build /app/.output ./.output
+EXPOSE 3000
+CMD ["node", ".output/server/index.mjs"]