Party wizard UX improvements

This page is a capture in the next bucket of the product backlog — a pre-sprint idea, not yet pulled into a sprint as a story.

Follow-on UX polish for the three-level provisioning wizard, deferred from the three-level provisioning plan (Phase 4).

Tasks

[ ] Force password reset: add password_reset_required = true flag to accounts created by provision-parties; auth_handler.hpp already handles this flag
[ ] Multi-select LEI picker: extend LeiEntityPicker from single- to multi-select so PartyProvisionPage can select a full GLEIF hierarchy in one pass
[ ] Per-party credential override: allow each PartyProvisionPage entry to override the shared username/password with per-party credentials
[ ] Async wizard progress: switch provision-parties to async for hierarchies > 20 parties — return workflow_id immediately and poll workflow.v1.status from the wizard progress page