Add libportaudio2 for sounddevice (daemon audio init)

The daemon's MujocoBackend initializes audio via sounddevice even
in sim mode, which requires the PortAudio library at import time.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Dockerfile.demo

@@ -11,6 +11,7 @@ FROM python:3.12-slim
 # libosmesa6-dev   — headless OpenGL for MuJoCo (no GPU needed)
 # libgl1           — GL shared libs (MuJoCo runtime dependency)
 # libglib2.0-0     — GLib2 (OpenCV runtime needs libgthread-2.0.so)
+# libportaudio2    — PortAudio (sounddevice library, daemon audio init)
 # tmux             — shell tab uses shared tmux sessions
 # curl             — startup script health checks
 # supervisor       — manages daemon + app lifecycle
@@ -19,6 +20,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     libosmesa6-dev \
     libgl1 \
     libglib2.0-0 \
+    libportaudio2 \
     tmux \
     curl \
     supervisor \