Add officer-slskd, a singleton sidecar that reverse-proxies to a
self-hosted slskd (Soulseek) instance and reports its loopback port to
the API on connect. All slskd knowledge (URL + API key) lives in the
sidecar; the platform is a thin auth+forward proxy for /api/slskd/* and
holds no slskd credentials. Mirrors the officer-vault pattern.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>