Add Heltec WiFi LoRa 32 V4.3 support

[waiet]

Summary

Add native OpenMQTTGateway support for the Heltec WiFi LoRa 32 V4.3 high-frequency board (ESP32-S3R2, SX1262, KCT8103L, 16 MB flash, 2 MB QSPI PSRAM), while preserving the existing Arduino-LoRa implementation for SX127x-based boards. V4.2/GC1109 and V4 R8 are not covered.

What changed

• add a dedicated PlatformIO board definition and heltec-wifi-lora-32-v4 environment
• add an SX1262 backend based on RadioLib, selected only by the V4 environment
• keep existing LoRa environments on the current Arduino-LoRa backend
• configure the V4 RF front end (KCT8103L control pins, RX/TX switching and PA-aware output-power mapping)
• retain DIO2 RF-switch control, set the chip current limit to 140 mA and TCXO to 1.8 V, and apply Heltec's mandatory RX workaround using a checked read-modify-write of register 0x08B5
• expose optional rxboostedgain through existing MQTT commands, state, NVS and a V4-only WebUI checkbox; default off, including migration of old NVS records
• initialize the V4 OLED power rail before display reset
• validate runtime LoRa configuration before applying or persisting it
• constrain this board to 863-928 MHz, 4-28 dBm requested connector output, SF5-12, CR5-8, preamble 6-65535 and supported discrete bandwidths; restore the previous hardware configuration after a failed update, or mark the radio unavailable if recovery fails
• stream WebUI power options in bounded chunks so the extended selector cannot truncate the page
• enforce the LoRa packet-size limit and preserve text/hex MQTT payload compatibility
• document the V4 environment, wiring profile and supported radio settings
• add host-side regression tests for both radio backends, payload bounds, configuration limits and non-LoRa build isolation
• retain the original ESP32 internal-temperature register implementation and use the Arduino temperature driver on ESP32-S3/newer targets

Compatibility

The radio abstraction is compile-time selected. Existing SX127x boards continue to use sandeepmistry/LoRa; RadioLib is linked only by the Heltec V4 environment. Builds without ZgatewayLORA do not require either LoRa library.

Existing MQTT topics and text/hex payload formats are unchanged. SX127x WebUI frequency/power/SF choices and state schema remain unchanged. The V4.3 profile defaults to 868 MHz, 14 dBm connector output, SF7, 125 kHz, CR4/5, preamble 8, sync word 0x12, CRC on, IQ inversion off and RX boost off. Hardware maximum settings are not a statement of regulatory permission.

Validation

• host tests: exact configuration bounds/discrete bandwidths, PA power mapping, payload codec, SX127x facade, SX1262 initialization, checked RX register operations, boost switching, rollback/recovery failure, non-LoRa isolation
• actual production JSON/NVS/state and WebUI handler tests using ArduinoJson 6.18.5: partial updates, old-record migration, rejected settings not persisted, save/load/init/erase, checkbox on/off, both radio profiles and the 3000-byte chunk bound
• PlatformIO builds:
  • heltec-wifi-lora-32-v4
  • heltec-wifi-lora-32
  • ttgo-lora32-v1
  • ttgo-lora32-v21
  • esp32dev-ble
• dependency check: RadioLib 7.7.1 only in the V4 build; Arduino-LoRa only in the three legacy LoRa builds
• git diff --check, shell syntax check and board JSON validation

Fresh hardware flashing and offline validation passed on two Heltec V4.3 868 MHz boards. Each reports 16 MB flash, 2 MB PSRAM, an OLED I2C acknowledgement and ready SX1262 with no radio error. A temporary serial-only adapter invoked the production LoRa command handler and observed its normal received-message queue/dispatch; neither this adapter nor offline overrides are included in the PR.

All 38 sequential test packets were received in both directions at 4 dBm requested connector output: normal/boosted/normal RX gain, SF5 and SF12, 15500/15600 Hz bandwidth interoperability and binary hex payloads. RSSI/SNR metadata, invalid-frequency rejection and NVS save/load passed. Previous LoRa settings were restored after testing. This is a close-range functional check, not a long-range, sensitivity, calibrated power or loss-rate measurement.

Live MQTT broker/WebUI end-to-end checks and outdoor range validation remain pending; this PR stays draft. No private Xiaomi BLE/offline dashboard features are included.

Run bash test/host/run_heltec_v4_radio_tests.sh after the V4 PlatformIO build has installed ArduinoJson, or set ARDUINOJSON_INCLUDE to its src directory. Local formatter checks, shell syntax, board JSON validation and git diff --check also passed. A final clean production V4.3 rebuild passed after all temporary hardware hooks were removed. Upstream clang-format 9 and security checks passed on 24ef8e3; the V4.3 matrix build is still queued, so its result is not yet claimed.

Relation to #2339

#2339 implements an SX1262 FSK weather-sensor gateway. This change targets the existing OpenMQTTGateway LoRa transport and adds a native V4 board/environment instead of using the V3 board definition as a pin-compatible workaround. The changes are complementary, although they touch some of the same board setup files.