Cut Vox to /v1/linked-services; remove /v1/vox/links alias

[Teagan42]

What to build

Retire the historical /v1/vox/links endpoint. Vox's client now calls /v1/linked-services (via the shared module from #157). Remove the alias handler from Conduit; a fresh Vox install must succeed against a Conduit that no longer exposes the old path.

Acceptance criteria

• POST /v1/vox/links returns 404 (route removed, not just deprecated).
• git grep -F "vox/links" returns zero hits outside CHANGELOG / historical spec references.
• Vox linking to a freshly-built Conduit works end-to-end (link, list, panel appears, proxied UI loads).
• DELETE /v1/vox/links/{peer_id} also removed; peer-revoke uses DELETE /v1/linked-services/{peer_id}.
• Release notes / CHANGELOG entry naming the breaking change and pointing at spec 0005.

Blocked by

• Extract shared Python link module; migrate Vox to it #157 — Extract shared Python link module; migrate Vox to consume it.