fix: move media server to 8093 — YOURLS/Apache owns 8092 on xNAS

The Unraid deployment's /media/api requests were answered by an
Apache/YOURLS stack squatting on 8092, surfacing as UI 503s; the CI
healthcheck (curl without -f) counted that 503 as healthy, so run #15
deployed green against a broken media server.

- media server port 8092 -> 8093 everywhere (server, MCP, agent, nginx,
  compose, CI, .env.example, docs, tests).
- healthchecks use curl -f in compose and rebuild.yml so HTTP error
  statuses fail deployment.
- tests default to the Unraid deployment (VOICE_WEB_URL=
  https://192.168.86.2:9178); token goes through nginx (loopback :8091
  is unreachable off-host); bind-mount-coupled tests skip on remote
  targets. AGENTS.md documents the convention and both failure modes.

docker-compose.yml

@@ -19,7 +19,7 @@ services:
       VOICE_USERS_FILE: "/etc/hope/users.json"
       VOICE_DEFAULT_USER: "${VOICE_DEFAULT_USER:-shane}"
       MEDIA_DIR: "/data/media"
-      MEDIA_SERVER_PORT: "${MEDIA_SERVER_PORT:-8092}"
+      MEDIA_SERVER_PORT: "${MEDIA_SERVER_PORT:-8093}"
       YTDLP_COOKIES: "${YTDLP_COOKIES:-/data/media/cookies.txt}"
     volumes:
       - ./livekit.yaml:/etc/livekit.yaml:ro
@@ -27,7 +27,7 @@ services:
       - ./skills:/skills
       - ./media:/data/media
     healthcheck:
-      test: ["CMD-SHELL", "curl -sk https://localhost:$${WEB_PORT:-9178}/ -o /dev/null && curl -s http://localhost:7880/ -o /dev/null && curl -s http://localhost:$${MEDIA_SERVER_PORT:-8092}/media/api/healthz -o /dev/null"]
+      test: ["CMD-SHELL", "curl -sfk https://localhost:$${WEB_PORT:-9178}/ -o /dev/null && curl -sf http://localhost:7880/ -o /dev/null && curl -sf http://localhost:$${MEDIA_SERVER_PORT:-8093}/media/api/healthz -o /dev/null"]
       interval: 15s
       timeout: 5s
       retries: 3