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/portal/server/api/tenants/[slug]/scheduling/[...path].ts

@@ -0,0 +1,34 @@
+// Catch-all proxy for the dezky Scheduling admin API. Forwards any method under
+// /api/tenants/:slug/scheduling/** to platform-api's
+// /api/v1/tenants/:slug/scheduling/** with the signed-in user's access token;
+// platform-api enforces tenant membership. Upstream status codes are preserved
+// so the admin UI sees real 400/403/404/409 responses.
+
+import { getUserSession } from 'nuxt-oidc-auth/runtime/server/utils/session.js'
+
+export default defineEventHandler(async (event) => {
+  const session = await getUserSession(event).catch(() => null)
+  const accessToken = (session as { accessToken?: string } | null)?.accessToken
+  if (!accessToken) {
+    throw createError({ statusCode: 401, statusMessage: 'Not signed in' })
+  }
+  const slug = getRouterParam(event, 'slug')
+  const path = getRouterParam(event, 'path') ?? ''
+  const base = process.env.PLATFORM_API_INTERNAL_URL ?? 'http://platform-api:3001'
+  const method = event.method
+  const query = getQuery(event)
+  const body = ['POST', 'PUT', 'PATCH'].includes(method) ? await readBody(event).catch(() => undefined) : undefined
+
+  try {
+    return await $fetch(`${base}/api/v1/tenants/${slug}/scheduling/${path}`, {
+      method: method as any,
+      query,
+      body,
+      headers: { Authorization: `Bearer ${accessToken}` },
+    })
+  } catch (err: any) {
+    const status = err?.response?.status ?? 502
+    const raw = err?.data?.message ?? err?.response?._data?.message ?? 'Upstream error'
+    throw createError({ statusCode: status, statusMessage: Array.isArray(raw) ? raw.join(', ') : String(raw) })
+  }
+})