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.

tests/test_web_ui.py

@@ -54,8 +54,11 @@ def test_livekit_client_bundle_serves(client):
 
 
 def test_token_endpoint_direct():
-    """Token server on 127.0.0.1:8091 (host network mode)."""
-    resp = httpx.post("http://127.0.0.1:8091/token", json={}, timeout=10)
+    """Token endpoint via TOKEN_URL (nginx path on remote deployments,
+    loopback :8091 when VOICE_TOKEN_URL points at the deployment host)."""
+    import conftest
+
+    resp = httpx.post(conftest.TOKEN_URL, json={}, timeout=10, verify=False)
     assert resp.status_code == 200
     data = resp.json()
     assert "token" in data and data["token"].count(".") == 2  # JWT shape