Add serial dev commands and a serial log helper

The firmware accepts burst, key <name>, sound on|off and short|normal
over serial, so UI behaviour can be reproduced on the device without
the keyboard. scripts/serial_log.sh records (and drives) it in a named
container that flash.sh removes before uploading.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

scripts/serial_log.py

@@ -0,0 +1,30 @@
+# Reads the Cardputer's serial port, reconnecting when it re-enumerates. Run via serial_log.sh.
+import glob, os, sys, time
+import serial
+
+end = time.time() + float(sys.argv[1])
+commands = sys.argv[2:]  # sent once after connecting, e.g. "burst"
+while time.time() < end:
+    ports = glob.glob('/dev/serial/by-id/*Espressif*')
+    if not ports:
+        time.sleep(1)
+        continue
+    try:
+        s = serial.Serial(os.path.realpath(ports[0]), 115200, timeout=0.2)
+        print('[connected]', flush=True)
+        for c in commands:  # "sleep:N" waits N seconds between commands
+            if c.startswith('sleep:'):
+                time.sleep(float(c[6:]))
+                continue
+            time.sleep(1)
+            s.write((c + '\n').encode())
+        commands = []
+        buf = b''
+        while time.time() < end:
+            buf += s.read(512)
+            while b'\n' in buf:
+                line, buf = buf.split(b'\n', 1)
+                print(line.decode(errors='replace').rstrip(), flush=True)
+    except Exception as e:
+        print('[disconnected]', e, flush=True)
+        time.sleep(1)