Wire KYC and Users modules to real backend API

• KYC module: replaced inline mock logic with a full service layer (kycApiClient, kycService), typed DTOs (kyc.types.ts), and React Query hooks (useKycDossiers). Pages (KycDossiersPage, KycDossierDetailPage) and KycStatisticsWidget now consume live data instead of the local mock array.

• Users module: same pattern applied — usersApiClient, userService, adminUserService, user.types.ts, and hooks (useUsers, useAdminUsers). UsersListPage, UserDetailPage, and AdminUsersPage migrated to TanStack Query.

• Endpoints: added /api/backoffice/kyc and /api/backoffice/users routes to endpoints.ts.

• AlertCard: converted <button> to <div role="button"> to fix interactive-element nesting (button-in-button) reported by the linter.