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/types/booking.ts

@@ -0,0 +1,42 @@
+// Shapes returned by the public scheduling API (mirrors platform-api's
+// PublicSchedulingController response mappers).
+
+export interface Branding {
+  tenantSlug: string
+  name: string
+  brandColor: string | null
+}
+
+export interface PublicInfo {
+  branding: Branding
+  host: { slug: string; displayName: string; timezone: string }
+  eventType: {
+    slug: string
+    title: string
+    description: string | null
+    durationMinutes: number
+    locationType: string
+  }
+}
+
+export interface SlotsResponse {
+  timezone: string
+  durationMinutes: number
+  slots: Array<{ startUtc: string; endUtc: string }>
+}
+
+export interface PublicBooking {
+  manageToken: string
+  status: 'pending' | 'confirmed' | 'cancelled' | 'rescheduled'
+  startUtc: string
+  endUtc: string
+  attendeeName: string
+  attendeeEmail: string
+  attendeeTimezone: string
+  attendeeNotes: string | null
+  locationType: string | null
+  locationUrl: string | null
+  branding: Branding
+  host: { slug: string; displayName: string; timezone: string }
+  eventType: { slug: string; title: string; durationMinutes: number }
+}