feat(versioning): REST API endpoints + restore commands

Exposes the version surface as three new endpoints per entity type
(chart, dashboard, dataset), each carrying the standard Superset
decorator stack (``@protect()``, ``@safe``, ``@statsd_metrics``,
``@event_logger.log_this_with_context``) so they appear in FAB's
``action_log`` alongside other audited operations.

| Method | Path | Purpose |
|---|---|---|
| GET  | ``/api/v1/{resource}/<uuid>/versions/`` | List version history (oldest-first; per entry: ``version_uuid``, ``version_number``, ``transaction_id``, ``operation_type``, ``issued_at``, ``changed_by``, ``changes`` array) |
| GET  | ``/api/v1/{resource}/<uuid>/versions/<version_uuid>/`` | Read-only snapshot of the entity at the requested version (scalar fields plus ``columns`` / ``metrics`` for datasets) |
| POST | ``/api/v1/{resource}/<uuid>/versions/<version_uuid>/restore`` | Replay the snapshot onto the live entity via Continuum's ``Reverter`` (non-destructive — produces a new version row stamping the restoring user via the standard save path) |

``<version_uuid>`` is a deterministic ``UUIDv5(entity_uuid,
transaction_id)`` so it's stable across replicas and retention
pruning. Authorisation reuses the resource's existing ``can_write``
permission; workspace admins can list / restore any entity.

**Restore commands** — ``superset/commands/{chart,dashboard,dataset}/
restore_version.py`` wrap ``VersionDAO.restore_version`` in the
standard ``@transaction()`` boundary. The command resolves the
``Reverter`` once per related collection (split-revert pattern, with
``flush + expire`` between calls) so a multi-relation restore
doesn't trip Continuum's autoflush race that would otherwise mark
half the collection as ``state.deleted=True`` mid-revert.

**Save responses** — ``PUT /api/v1/{resource}/<pk>`` is updated to
include ``old_version`` / ``new_version`` (0-based numbers),
``old_transaction_id`` / ``new_transaction_id`` (stable across
pruning), and ``old_version_uuid`` / ``new_version_uuid`` body
fields so callers can correlate a save with its resulting version
row. The ``ETag`` response header in the next commit is built on
top of this, but the body fields stay — they predate the header
and remain useful for clients that don't read response headers.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>