Fix demo: use latest reachy-mini, skip media in DEMO_MODE

- Switch back to latest reachy-mini (1.3.1) — the Zenoh pub_status
error was a race condition from double-starting the daemon, not a
version bug. The startup script already avoids double-start.
- Add DEMO_MODE env var to Dockerfile + app.py check: when set,
request_media_backend="no_media" skips camera/audio init that
fails in headless containers (UDP camera stream not available).

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

Dockerfile.demo

@@ -28,6 +28,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 # MuJoCo headless rendering — OSMesa software renderer, no GPU required
 ENV MUJOCO_GL=osmesa
+# Demo mode — skips hardware media (camera/audio) in app init
+ENV DEMO_MODE=1
 
 # HuggingFace Spaces requires non-root user with uid 1000
 RUN useradd -m -u 1000 user
@@ -37,7 +39,7 @@ ENV PATH="/home/user/.local/bin:${PATH}"
 WORKDIR /home/user/app
 
 # Install MuJoCo + reachy-mini SDK (provides reachy-mini-daemon command)
-RUN pip install --no-cache-dir --user mujoco "reachy-mini>=1.2.8,<1.3"
+RUN pip install --no-cache-dir --user mujoco "reachy-mini"
 
 # Copy the hello_world app and install as editable package
 # (editable so the daemon discovers it via entry points)

hello_world/app.py

@@ -8,6 +8,7 @@ Provides a Status dashboard with system telemetry and robot state.
 __all__ = ['HelloWorld']
 
 import logging
+import os
 import threading
 import time
 import urllib.request
@@ -37,6 +38,7 @@ class HelloWorld(ReachyMiniApp):
     """A developer dashboard app for Reachy Mini with system telemetry."""
 
     custom_app_url: str | None = "http://0.0.0.0:8042"
+    request_media_backend: str | None = "no_media" if os.environ.get("DEMO_MODE") else None
 
     def __init__(self):
         super().__init__()