docs(livekit): bind lk-jwt-service to 127.0.0.1:8071, not all interfaces (#24)

voice-limit-guard (:8070) is meant to be the only way to get a LiveKit
token, but lk-jwt-service bound :8071 on every interface, so any LAN
host could mint an unguarded token (no max_users, full publish sources
in audio-only rooms). The guard runs on the same LXC: document the
loopback bind in the setup steps and the port table.

Refs #24

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

README.md

@@ -67,7 +67,7 @@ matrix/
 - coturn config: `/etc/turnserver.conf`
 - LiveKit config: `/etc/livekit/config.yaml`
 - LiveKit service: `livekit-server.service`
-- lk-jwt-service: `lk-jwt-service.service` (now binds `:8071` via drop-in `/etc/systemd/system/lk-jwt-service.service.d/override.conf`; serves JWT tokens for MatrixRTC at `/sfu/get` and legacy `/get_token`)
+- lk-jwt-service: `lk-jwt-service.service` (now binds `127.0.0.1:8071` via drop-in `/etc/systemd/system/lk-jwt-service.service.d/override.conf`; serves JWT tokens for MatrixRTC at `/sfu/get` and legacy `/get_token`)
 - voice-limit-guard: `voice-limit-guard.service` (binds `:8070`, fronts lk-jwt-service — enforces hard per-room voice participant limits **and publish permissions (screenshare/camera via JWT re-signing)** for ALL clients; script `/opt/voice-limit-guard/voice-limit-guard.py`) — see [Voice Channel Limits & Call Permissions](#voice-channel-limits--call-permissions)
 - Hookshot: `/opt/hookshot/`, service: `matrix-hookshot.service`
 - Hookshot config: `/opt/hookshot/config.yml`
@@ -238,7 +238,9 @@ install -D -m644 /opt/matrix-config/livekit/voice-limit-guard.py /opt/voice-limi
 install -m644 /opt/matrix-config/systemd/voice-limit-guard.service /etc/systemd/system/voice-limit-guard.service
 # one-time: rebind lk-jwt-service to :8071
 mkdir -p /etc/systemd/system/lk-jwt-service.service.d
-printf '[Service]\nEnvironment=LIVEKIT_JWT_BIND=:8071\n' > /etc/systemd/system/lk-jwt-service.service.d/override.conf
+# Loopback only (matrix #24): the guard runs on this LXC; binding all
+# interfaces let any LAN host mint unguarded tokens straight from :8071.
+printf '[Service]\nEnvironment=LIVEKIT_JWT_BIND=127.0.0.1:8071\n' > /etc/systemd/system/lk-jwt-service.service.d/override.conf
 systemctl daemon-reload && systemctl restart lk-jwt-service && systemctl enable --now voice-limit-guard
 ```
 
@@ -290,7 +292,7 @@ The token in `draupnir/production.yaml` in this repo is **intentionally redacted
 | 7880 | LiveKit HTTP | 0.0.0.0 |
 | 7881 | LiveKit RTC TCP | 0.0.0.0 |
 | 8070 | voice-limit-guard (fronts lk-jwt-service) | 0.0.0.0 |
-| 8071 | lk-jwt-service (behind guard) | 0.0.0.0 |
+| 8071 | lk-jwt-service (behind guard) | 127.0.0.1 (matrix #24; was 0.0.0.0) |
 | 8080 | synapse-admin (nginx) | 0.0.0.0 |
 | 3478 | coturn STUN/TURN | 0.0.0.0 |
 | 5349 | coturn TURNS/TLS | 0.0.0.0 |