audio: add PipeWire+BT audio-bridge, mopidy (Qobuz+local), librespot (Spotify Connect)

- audio-bridge: alpine + pipewire + pipewire-pulse + wireplumber + bluez + dbus + tini
  Routes audio from librespot/mopidy/phone-BT to USB DAC (Q5K) via ALSA.
  Privileged + host network for bluetoothd HCI access.
- mopidy: built from python:3.12-slim-bookworm + pip (no ghcr.io dep).
  Qobuz (auth from developer.qobuz.com) + local files. PA bridge to audio-bridge.
- librespot: built from rust:1.85.1 on RPi (cross-compile too slow under qemu).
  Spotify Connect target named 'Klubhaus'. PA bridge to audio-bridge.

Both mopidy and librespot build locally to avoid ghcr.io auth/rate-limit issues.
PEQ stays on Q5K side (Qudelix app, 20 bands) for source-independent EQ.

infra/mopidy/Dockerfile

@@ -0,0 +1,32 @@
+# Mopidy music server with Qobuz + local files
+# Builds from python:3.12-slim + pip (no ghcr.io dependency)
+
+FROM python:3.12-slim-bookworm
+
+# System deps for mopidy + extensions + GStreamer playback
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends \
+      gstreamer1.0-tools \
+      gstreamer1.0-plugins-good \
+      gstreamer1.0-plugins-bad \
+      libcairo2 \
+      libpango-1.0-0 \
+      libpangoft2-1.0-0 \
+      libgirepository1.0-dev \
+ && rm -rf /var/lib/apt/lists/*
+
+RUN pip install --no-cache-dir \
+    Mopidy==3.4.2 \
+    Mopidy-Qobuz \
+    Mopidy-Local
+
+# Default config (overridable via bind mount)
+COPY mopidy.conf /config/mopidy.conf
+
+VOLUME ["/var/lib/mopidy", "/music"]
+EXPOSE 6680
+
+# Run as the unprivileged "mopidy" user from python base
+USER nobody
+
+CMD ["mopidy", "--config", "/config/mopidy.conf"]