The per-board libs (M5Stack/M5StickC/M5StickC-Plus/M5Tough) don't build on
Arduino core 3.x, which kept the five M5 BLE envs pinned to espressif32@6.1.0.
Port board support to M5Unified + M5GFX so they run ${com.esp32_platform} like
the rest of the tree.
- environments.ini: 5 M5 envs -> modern platform + m5unified. m5stick-c uses the
pico32 variant (m5stick_c variant absent upstream) and no_coredump partitions
(M5Unified overflows min_spiffs).
- boardM5.cpp / config_M5.h: single <M5Unified.h>; M5.Lcd aliases M5.Display;
unified brightness/sleep/wake.
- main.cpp / mqttDiscovery.cpp: battery telemetry via M5.Power; AXP192-only
Vin/VBus/temp fields dropped (no portable equivalent).
All five M5 envs build; M5Stack Core hardware-verified.
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>