feat: add mock Teensy support with entrypoint and LTC generator

Co-authored-by: aider (openai/gpt-5) <aider@aider.chat>

scripts/entrypoint.sh

@@ -0,0 +1,27 @@
+#!/bin/sh
+set -eu
+
+# If enabled, start a mock Teensy that exposes a PTY at /dev/ttyACM0 and streams LTC-like lines.
+if [ "${MOCK_TEENSY:-0}" = "1" ]; then
+  echo "[entrypoint] Starting mock Teensy (PTY at /dev/ttyACM0)..." >&2
+  # Bridge the LTC generator to a PTY that looks like a Teensy serial port.
+  # Left side runs the generator, right side is a PTY linked to /dev/ttyACM0
+  socat -d -d -lf /dev/stderr EXEC:'/usr/local/bin/ltc-gen.sh',pty,ctty,echo=0,raw PTY,link=/dev/ttyACM0,raw,echo=0 &
+  SOCAT_PID=$!
+
+  # Wait briefly for the PTY to appear
+  i=0
+  while [ $i -lt 50 ]; do
+    if [ -e /dev/ttyACM0 ]; then
+      break
+    fi
+    i=$((i+1))
+    sleep 0.1
+  done
+  if [ ! -e /dev/ttyACM0 ]; then
+    echo "[entrypoint] WARNING: Failed to create /dev/ttyACM0 (mock Teensy)" >&2
+  fi
+fi
+
+# Run the requested command (default: get-haci)
+exec "$@"