chore(changeset): record the ADR-0087 disposition for the list() narrowing

`check-adr-0087-registration` requires a declared-breaking changeset to answer
the ledger question in writing. No authorable key, Zod schema or stored row
moves here, and a tree carrying one of the two shapes needs the FILE relocated
rather than any document rewritten — nothing `objectstack migrate meta` can
project, so the disposition is `not-required (no-migration-prescription)`.

Part of #14486

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0112hMx9hjJ9BgB28X97DS68

Author: claude

.changeset/filesystem-loader-list-reachability.md

@@ -34,3 +34,5 @@ serializers, not §10's `.json`-only rule, which governs the `metadata-fs` store
 `loadMany()` is unchanged and still returns bodies for nested and
 extension-less files; `findFile()` still resolves an explicitly path-shaped
 name such as `crm/account`, which nothing lists.
+
+<!-- adr-0087: not-required (no-migration-prescription) No authorable key, Zod schema or stored row moves: this narrows one runtime loader's `list()` output. The ledger's artifacts project metadata rewrites, and there is nothing here for `objectstack migrate meta` to rewrite — a tree carrying a nested or extension-less file needs the FILE relocated into the two-segment layout ADR-0008 §10 already prescribes, which no migration prescription can express. -->