audio-bridge: start pipewire-pulse separately with TCP 4713 listener

Alpine's pipewire-pulse package ships the daemon binary but doesn't
auto-load the PA bridge module on alpine. We need to start pipewire-pulse
as a separate process with -a tcp:4713 so PA clients (librespot, mopidy)
can connect via TCP.

Layout:
- pipewire: audio server (native protocol)
- pipewire-pulse: PA-compat bridge, listens on tcp:4713 + unix:/tmp/pulse-socket
- wireplumber: session manager (loads BT modules, hot-plug handling)

infra/audio-bridge/entrypoint.sh

@@ -35,5 +35,11 @@ fi
 wireplumber &
 sleep 1
 
-# PipeWire last. pipewire-pulse auto-loads PA bridge so clients connect via TCP 4713.
-exec pipewire
+# PipeWire (audio server). Listens on its own native socket.
+pipewire &
+
+# PipeWire-Pulse daemon: PA-compatible bridge. Listen on TCP 4713 so PA clients
+# (librespot, mopidy) can connect from sibling containers without unix socket
+# path coupling.
+sleep 1
+exec pipewire-pulse -a tcp:4713 -a unix:/tmp/pulse-socket