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.

.gitea/workflows/rebuild.yml

@@ -26,7 +26,7 @@ jobs:
             --name voice \
             --network host \
             --restart unless-stopped \
-            --health-cmd='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' \
+            --health-cmd='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' \
             --health-interval=15s \
             --health-timeout=5s \
             --health-retries=3 \
@@ -50,7 +50,7 @@ jobs:
             -e VOICE_USERS_FILE=/etc/hope/users.json \
             -e VOICE_DEFAULT_USER=shane \
             -e MEDIA_DIR=/data/media \
-            -e MEDIA_SERVER_PORT=8092 \
+            -e MEDIA_SERVER_PORT=8093 \
             -e YTDLP_COOKIES=/data/media/cookies.txt \
             hope-voice-api-voice:latest