Initial commit: Arduino Uno Q USB Audio Synth project

- USB gadget (UAC1 + MIDI) with boot persistence
- USB host mode with auto-detection
- Pure Data synth patch with ALSA + UDP netreceive MIDI input
- MIDI rawmidi-to-UDP bridge (midi-bridge.py)
- LED matrix visualization (led-matrix-viz.py via arduino-router RPC)
- MCU sketch for LED matrix control (Arduino_RouterBridge + ArduinoGraphics)
- Conftest/OPA Rego policy validation suite for .pd files
- gen_synth_pd.py: programmatic .pd file generator
- System services: midi-bridge, led-matrix-viz, pd-synth-auto, usb-role-detect
- Justfile with deploy, enable, diagnostic recipes
- Diagnostic script (diag.sh)

system/configure-usb-host.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+# configure-usb-host.sh — Wait for USB audio interface in host mode.
+# Finds the first USB audio capture/playback device and writes device
+# info to /run/usb-audio-dev for Pd to use.
+#
+# When the Uno Q acts as USB host (MIDI controller + USB audio interface
+# connected via hub), the USB audio interface appears as a ALSA card
+# driven by snd-usb-audio.
+
+set -euo pipefail
+
+DEV_FILE="/run/usb-audio-dev"
+POLL_SECONDS=10
+
+die() { echo "[USB-HOST] $*" >&2; exit 1; }
+info() { echo "[USB-HOST] $*"; }
+
+info "Waiting for USB audio interface..."
+
+for ((i = 0; i < POLL_SECONDS; i++)); do
+    # Look for USB audio cards (not UAC1Gadget, not internal)
+    cards=$(aplay -l 2>/dev/null | grep -i "usb" | grep -vi "gadget" || true)
+    if [ -n "$cards" ]; then
+        # Pick the first USB audio card
+        card=$(echo "$cards" | head -1 | awk '{print $2}' | tr -d ':')
+        info "Found USB audio card: $card"
+        echo "hw:$card,0" > "$DEV_FILE"
+        cat "$DEV_FILE"
+        exit 0
+    fi
+    # Also check if any MIDI devices appeared
+    if command -v aseqdump &>/dev/null; then
+        midi_ports=$(aconnect -i -o -l 2>/dev/null | grep -i "usb" | head -1 || true)
+        if [ -n "$midi_ports" ]; then
+            info "Found USB MIDI device: $midi_ports"
+        fi
+    fi
+    sleep 1
+done
+
+die "No USB audio interface found after ${POLL_SECONDS}s (connect one and restart)"