beta/v1: paginate ClientViewSet and add client_name to SiteSerializer

[jbloomfield80]

Summary

Two small consistency fixes to the beta/v1 API:

1. ClientViewSet is now paginated, matching SiteViewSet.
2. The beta SiteSerializer now includes client_name.

Motivation

Within beta/v1, the viewsets are inconsistent: SiteViewSet uses StandardResultsSetPagination (and search/ordering), but ClientViewSet has none, so GET /beta/v1/client/ returns a bare JSON array while GET /beta/v1/site/ returns the standard DRF envelope (count/next/previous/results).

This breaks external tooling that consumes the paginated beta API. Iintegrating Organization Mappings in Rewst (which expects a paginated, array-yielding endpoint) fails against /beta/v1/client/ with:

list indices must be integers or slices, not str

because the client list response isn't the paginated object shape the tooling expects. Separately, the beta SiteSerializer (fields = "__all__") only carries the client FK id, so consumers can't display the client name without a second lookup even though the legacy clients API exposes client_name.

Changes

• beta/v1/client/views.py add pagination_class = StandardResultsSetPagination to ClientViewSet, plus the same DjangoFilterBackend/SearchFilter/OrderingFilter setup SiteViewSet already uses, with ordering = ["id"] for stable paging.
• beta/v1/serializers.py add client_name = serializers.CharField(source="client.name", read_only=True) to SiteSerializer.

Behavior / compatibility

• Response-shape change: GET /beta/v1/client/ now returns the paginated
  envelope ({count, next, previous, results: [...]}) instead of a bare array.
  Callers must read .results. This aligns it with the sibling site endpoint and
  the documented DRF pagination behavior. Scoped to the experimental beta/v1
  namespace.
• SiteViewSet already returned the paginated shape, so its only change is the
  added read-only client_name field.
• page_size defaults to 100 (max_page_size 1000) via the existing
  StandardResultsSetPagination.
• The OpenAPI schema (drf-spectacular) reflects the new paginated client response
  automatically, no manual schema changes needed.

Testing

• Verified GET /beta/v1/client/ returns the paginated envelope and honors
  ?page, ?page_size
• Verified GET /beta/v1/site/ includes client_name.
• Running in production after a snapshot, in addition to a separate test instance.

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