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)

pd-validator/test_bad.pd

@@ -0,0 +1,14 @@
+#N canvas 0 0 400 300 10;
+#X obj 20 20 notein;
+#X obj 80 20 osc~;
+#X connect 0 0 1 0;
+#X connect 0 1 1 1;
+#X connect 0 0 1 0;
+#X connect 99 0 1 0;
+#X connect 0 0 99 0;
+#X connect 0 0 0 0;
+#X connect 0 -1 1 0;
+#X obj 20 100 dac~;
+#X connect 1 99 3 0;
+#X connect 1 0 3 99;
+#X connect 1 0 3 0;