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/99-usb-role.rules

@@ -0,0 +1,15 @@
+# USB role change udev rule
+# Triggers role re-detection when USB-C cable is plugged/unplugged
+# or when USB devices are connected/disconnected in host mode.
+#
+# Install: sudo cp 99-usb-role.rules /etc/udev/rules.d/
+# Reload:  sudo udevadm control --reload-rules
+
+# USB gadget/UDC events (dwc3 role changes)
+ACTION=="change", SUBSYSTEM=="udc", RUN+="/usr/local/bin/on-usb-role-change.sh"
+
+# USB device connect/disconnect (host mode)
+ACTION=="add|remove", SUBSYSTEM=="usb", RUN+="/usr/local/bin/on-usb-role-change.sh"
+
+# USB audio card (host mode audio interface)
+ACTION=="add|remove", SUBSYSTEM=="sound", RUN+="/usr/local/bin/on-usb-role-change.sh"