feat(reservations): service + validators + exclusivity tests

Adds the berth_reservations service covering the full lifecycle
(pending -> active -> ended/cancelled) with tenant scoping, DB-enforced
exclusivity on the idx_br_active partial unique index, and
client-or-company-member cross-checks for yacht ownership.

- validators: createPending / activate / end / cancel / list schemas
- service: createPending, activate, endReservation, cancel, getById,
  listReservations — with narrow 23505/idx_br_active catch that
  re-queries the conflicting active reservation
- socket events: berth_reservation:{created,activated,ended,cancelled}
- tests: unit (lifecycle, tenant, membership cross-check),
  integration (concurrent-activate ConflictError + re-activate after end)

src/lib/socket/events.ts

@@ -107,6 +107,12 @@ export interface ServerToClientEvents {
     clientId: string;
   }) => void;
 
+  // Berth reservation events
+  'berth_reservation:created': (payload: { reservationId: string; berthId: string }) => void;
+  'berth_reservation:activated': (payload: { reservationId: string; berthId: string }) => void;
+  'berth_reservation:ended': (payload: { reservationId: string; berthId: string }) => void;
+  'berth_reservation:cancelled': (payload: { reservationId: string; berthId: string }) => void;
+
   // Document events
   'document:created': (payload: { documentId: string; type?: string; interestId?: string }) => void;
   'document:updated': (payload: { documentId: string; changedFields?: string[] }) => void;