Scaffold PlatformIO project with Docker-based build, test and flash

- pioarduino platform 55.03.312 (Arduino-ESP32 3.3.x / ESP-IDF 5.5),
  board m5stack-stamps3, M5Cardputer 1.1.1
- native env with Unity for host-side tests
- scripts/ci.sh and scripts/flash.sh run PlatformIO in a container
- version injected from git describe
- boot stub shows name, version and pressed keys
- GPL-3.0 license

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

platformio.ini

@@ -0,0 +1,27 @@
+; roro9stack — firmware for M5Stack Cardputer ADV + Cap LoRa-1262
+; Build/test/flash through scripts/ci.sh and scripts/flash.sh (Docker), see README.
+
+[platformio]
+default_envs = cardputer-adv
+
+[env]
+extra_scripts = pre:scripts/version.py
+test_framework = unity
+
+[env:cardputer-adv]
+platform = https://github.com/pioarduino/platform-espressif32/releases/download/55.03.312/platform-espressif32.zip
+board = m5stack-stamps3
+framework = arduino
+board_build.partitions = default_8MB.csv
+monitor_speed = 115200
+build_flags =
+    -DARDUINO_USB_CDC_ON_BOOT=1
+    -DARDUINO_USB_MODE=1
+lib_deps =
+    m5stack/M5Cardputer @ 1.1.1
+test_ignore = *
+
+; Host-side unit tests for pure logic (no hardware).
+[env:native]
+platform = native
+build_flags = -std=gnu++17