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/gen_mpk_sim.py

@@ -0,0 +1,120 @@
+#!/usr/bin/env python3
+"""Generate mpk-mini-sim.pd — MPK Mini Mk II simulator.
+
+Architecture: each key/pad has bng→t b b→msg for note-on, del→msg for note-off.
+All msgs connect to a single [netsend -u -b] via send/receive.
+Knobs: hsl→msg→[s $0-cc], central [r $0-cc]→netsend.
+"""
+from pathlib import Path
+
+SCRIPT_DIR = Path(__file__).resolve().parent
+OUTPUT = SCRIPT_DIR.parent / "pd" / "mpk-mini-sim.pd"
+
+def connect(c, src, sout, dst, din):
+    c.append((src, sout, dst, din))
+
+def Obj(o, x, y, *args):
+    idx = len(o)
+    o.append((x, y, *args))
+    return idx
+
+def gen():
+    o, c = [], []
+
+    # ── UDP sender (hardcoded IP — edit the msg box to change) ──
+    Obj(o, 10, 10, "loadbang")
+    Obj(o, 10, 30, "msg", ";")
+    msg_conn = Obj(o, 10, 50, "msg", "connect 192.168.9.167 8081;")
+
+    ns = Obj(o, 10, 80, "netsend", "-u", "-b")
+    connect(c, msg_conn, 0, ns, 0)
+
+    Obj(o, 200, 30, "text", "← edit this line to change target IP:port")
+    instr = Obj(o, 10, 440, "text", "Click keys to play. Knobs send CC on change. IPS (192.168.9.167:8081)")
+    instr2 = Obj(o, 10, 460, "text", "MIDI ch: 144=note-on ch1, 128=note-off ch1, 176=CC ch1")
+
+    # ── Keyboard: C3(48) to C5(72) ──
+    keys = [
+        ("C3",48),("C#3",49),("D3",50),("D#3",51),("E3",52),
+        ("F3",53),("F#3",54),("G3",55),("G#3",56),("A3",57),
+        ("A#3",58),("B3",59),
+        ("C4",60),("C#4",61),("D4",62),("D#4",63),("E4",64),
+        ("F4",65),("F#4",66),("G4",67),("G#4",68),("A4",69),
+        ("A#4",70),("B4",71),("C5",72),
+    ]
+
+    Obj(o, 20, 120, "text", "-- KEYBOARD --")
+    for i, (name, note) in enumerate(keys):
+        x = 30 + (i % 13) * 46
+        y = 140 + (i // 13) * 60
+        Obj(o, x, y, "text", name)
+        b = Obj(o, x, y+14, "bng", 15, 25, 0, 1, 0, 0, "empty", f"k{note}", -2,-8,0,10,-262144,-1,-1)
+        trig = Obj(o, x, y+44, "t", "b b")
+        msg_on = Obj(o, x, y+64, "msg", f"midi 144 {note} 100;")
+        msg_off = Obj(o, x, y+82, "msg", f"midi 128 {note} 0;")
+        del300 = Obj(o, x, y+100, "del", 300)
+        connect(c, b, 0, trig, 0)
+        connect(c, trig, 0, msg_on, 0)
+        connect(c, msg_on, 0, ns, 0)
+        connect(c, trig, 1, del300, 0)
+        connect(c, del300, 0, msg_off, 0)
+        connect(c, msg_off, 0, ns, 0)
+
+    # ── Pads (C2-G2, notes 36-43) ──
+    pads = [("C2",36),("C#2",37),("D2",38),("D#2",39),("E2",40),("F2",41),("F#2",42),("G2",43)]
+    Obj(o, 680, 120, "text", "-- PADS --")
+    for i, (name, note) in enumerate(pads):
+        x = 680 + (i % 4) * 55
+        y = 140 + (i // 4) * 55
+        Obj(o, x, y, "text", name)
+        b = Obj(o, x, y+14, "bng", 15, 15, 0, 1, 0, 0, "empty", f"p{note}", -2,-8,0,10,-262144,-1,-1)
+        trig = Obj(o, x, y+32, "t", "b b")
+        msg_on = Obj(o, x, y+52, "msg", f"midi 144 {note} 100;")
+        msg_off = Obj(o, x, y+70, "msg", f"midi 128 {note} 0;")
+        del200 = Obj(o, x, y+88, "del", 200)
+        connect(c, b, 0, trig, 0)
+        connect(c, trig, 0, msg_on, 0)
+        connect(c, msg_on, 0, ns, 0)
+        connect(c, trig, 1, del200, 0)
+        connect(c, del200, 0, msg_off, 0)
+        connect(c, msg_off, 0, ns, 0)
+
+    # ── Knobs (CC 1, 71-77) ──
+    knobs = [(1,"Mod",64),(71,"Reson",64),(72,"Release",64),(73,"Attack",64),
+             (74,"Cutoff",100),(75,"Decay",64),(76,"LFO Rate",64),(77,"LFO Depth",64)]
+    Obj(o, 20, 280, "text", "-- KNOBS --")
+    for i, (cc, name, init) in enumerate(knobs):
+        x = 30 + i * 85
+        y = 300
+        Obj(o, x, y, "text", f"CC{cc} {name}")
+        hsl = Obj(o, x, y+15, "hsl", 50, 10, 0, 127, init, 0, 0, "empty", f"cc{cc}", -2,-8,0,10,-262144,-1,-1,7200,1)
+        msg = Obj(o, x, y+30, "msg", f"midi 176 {cc} $1;")
+        connect(c, hsl, 0, msg, 0)
+        connect(c, msg, 0, ns, 0)
+
+    # ── Write (Pd format: #X obj for objects, #X msg/text/floatatom/symbol for others) ──
+    lines = ["#N canvas 0 0 950 490 10;"]
+    obj_types = {"bng","t","del","netsend","loadbang","hsl","comment"}
+    for x, y, *args in o:
+        etype = args[0]
+        rest = args[1:]
+        if etype in obj_types:
+            # Pd stores GUI objects as: #X obj x y <name> <args>
+            name = etype
+            if name == "comment": name = "text"  # Pd uses text for comments
+            joined = " ".join(str(a) for a in rest)
+            lines.append(f"#X obj {x} {y} {name} {joined};")
+        else:
+            joined = " ".join(str(a) for a in rest)
+            lines.append(f"#X {etype} {x} {y} {joined};")
+    for src, sout, dst, din in c:
+        lines.append(f"#X connect {src} {sout} {dst} {din};")
+    lines.append("")
+    return "\n".join(lines)
+
+if __name__ == "__main__":
+    content = gen()
+    OUTPUT.parent.mkdir(parents=True, exist_ok=True)
+    OUTPUT.write_text(content)
+    print(f"Wrote {OUTPUT}")
+    print(f"  {len(content.splitlines())} lines, {content.count('#X obj')} objects, {content.count('#X connect')} connections")