coreapi: regenerate client against current /repos spec + adapt callers

Regenerate the coreapi client from the updated upstream OpenAPI document (go generate ./internal/coreapi), picking up the /repos?scope=all directory shape, per-placement RepoPlacement fields (ClusterSlug/Cell/Jurisdiction/ Mirror), and the response-envelope changes (list bodies now nest under .Response). Deprecates the top-level RepoIndexEntry cell/slug fields and CreatedMirror.Empty.

Adapt existing callers to the new surface:

• org.go / resolveref.go: read list results off out.Response.*.
• search_cmd.go: pass coreapi.ListReposParams{} to ListRepos.
• repo_mirror_create_wizard.go / repo_mirror.go: nolint the deprecated CreatedMirror.Empty in the create flow (cleanup tracked separately).
• cell_fanout.go: route every placement by its own RepoPlacement.ClusterSlug (home and mirror alike) instead of taking the deprecated top-level slug for the home placement only, which left mirrors slugless and mis-routed a cross-jurisdiction mirror to the jurisdiction-default cell — a silent code- search miss. Tests updated to per-placement slugs.