auto-detect MIDI device, drop ALSA sequencer dependency, MPK Mini simulator

midi-bridge.py:
  - Auto-detect rawmidi device (gadget f_midi > env override > fallback)
  - Reconnect on ENODEV (device hotplug)
  - No longer needs MIDI_BRIDGE_DEV env var in common cases

start-synth.sh:
  - Remove all -alsamidi/-midiadddev flags (kernel lacks CONFIG_SND_SEQUENCER)
  - MIDI handled entirely by midi-bridge.service → UDP → netreceive
  - Host mode: same approach, no ALSA sequencer needed

mpk-mini-sim.pd:
  - New MPK Mini Mk II simulator (25 keys, 8 pads, 8 CC knobs)
  - Proper Pd #X obj format for all objects (bng, hsl, t, del, netsend, loadbang)
  - UDP output to board:8081, matching midi-bridge format

system: enable usb-gadget-audio.service at boot, load dwc3 module at boot

scripts/start-synth.sh

@@ -56,17 +56,11 @@ if [ "$MODE" = "auto" ]; then
                 ALSA_DEV=$(cat /run/usb-audio-dev)
             fi
             info "Mode: USB host (MIDI controller + USB audio interface)"
-            MIDI_OPTS=(-alsamidi)
-            midi_dev=$(amidi -l 2>/dev/null | grep -v "^Dir" | head -1 | awk '{print $2}' | sed 's/\(hw:[0-9]*,[0-9]*\).*/\1/')
-            if [ -n "$midi_dev" ]; then
-                MIDI_OPTS+=(-midiadddev "$midi_dev")
-                info "  MIDI device: $midi_dev"
-            fi
+            # MIDI handled by midi-bridge.service → UDP → Pd netreceive
             AUDIO_OPTS=(-audiooutdev 4 -audioindev 4)
             PD_ARGS=(
                 -nogui -alsa
                 -send "pd dsp 1"
-                "${MIDI_OPTS[@]}"
                 "${AUDIO_OPTS[@]}"
                 -audiobuf 20 -blocksize 64 -r 48000
                 -channels 2 -inchannels 0 -outchannels 2
@@ -87,18 +81,13 @@ fi
 
 # --- Configure per-mode options ---
 AUDIO_OPTS=()
-MIDI_OPTS=(-alsamidi)
 
 if [ "$MODE" = "usb" ]; then
     info "Mode: USB gadget (UAC1 audio + gmidi MIDI)"
     AUDIO_OPTS=(-audiooutdev 2 -audioindev 2)
     if aplay -l 2>/dev/null | grep -q "UAC1Gadget"; then
         info "  USB gadget: OK"
-        midi_dev=$(amidi -l 2>/dev/null | grep "f_midi" | head -1 | awk '{print $2}')
-        if [ -n "$midi_dev" ]; then
-            MIDI_OPTS+=(-midiadddev "$midi_dev")
-            info "  MIDI device: $midi_dev"
-        fi
+        # MIDI handled by midi-bridge.service → UDP → Pd netreceive
     else
         info "  USB gadget: NOT DETECTED (kernel modules needed)"
     fi
@@ -125,19 +114,12 @@ if [ "$MODE" = "loopback" ]; then
 fi
 
 PD_ARGS=(
-    -nogui
-    -alsa
-    "${MIDI_OPTS[@]}"
-    "${AUDIO_OPTS[@]}"
+    -nogui -alsa
     -send "pd dsp 1"
-    -audiobuf 20
-    -blocksize 64
-    -r 48000
-    -channels 1
-    -inchannels 0
-    -outchannels 1
-    -path "$PD_DIR"
-    "$PATCH"
+    "${AUDIO_OPTS[@]}"
+    -audiobuf 20 -blocksize 64 -r 48000
+    -channels 1 -inchannels 0 -outchannels 1
+    -path "$PD_DIR" "$PATCH"
 )
 
 if [ "$VERBOSE" = true ]; then