feat: add Heltec tracker MQTT observer builds

[yellowcooln]

PR Summary

Overview

This PR adds MQTT observer firmware targets for both the Heltec Wireless Tracker v1.1 and Heltec Wireless Tracker v2 platforms.

The implementation introduces a dedicated PlatformIO board definition for Tracker v1.1, reuses the existing Tracker v2 variant where the hardware is compatible, and updates FEM handling so both hardware revisions build correctly.

Changes

New MQTT Observer Build Targets

Added four new firmware environments:

• heltec_tracker_v1_1_repeater_observer_mqtt
• heltec_tracker_v1_1_room_server_observer_mqtt
• heltec_tracker_v2_repeater_observer_mqtt
• heltec_tracker_v2_room_server_observer_mqtt

Heltec Tracker v1.1 Support

• Added a PlatformIO board definition for Heltec Wireless Tracker v1.1.
• Reuses the existing Tracker v2 variant implementation where hardware behavior is identical.
• Minimizes code duplication between Tracker hardware revisions.

FEM Compatibility

Updated LoRaFEMControl.cpp so FEM control is only enabled when the required hardware is present.

This allows Tracker v1.1 to build successfully without the KCT8103L FEM control pins found on Tracker v2 hardware while preserving existing Tracker v2 behavior.

Documentation

• Updated MQTT_IMPLEMENTATION.md with the new MQTT observer firmware environments.

Files Changed

• boards/heltec_tracker_v1_1.json
• variants/heltec_tracker_v2/platformio.ini
• variants/heltec_tracker_v2/LoRaFEMControl.cpp
• MQTT_IMPLEMENTATION.md

Validation

Performed the following checks:

python3 -m json.tool boards/heltec_tracker_v1_1.json
git diff --check

Confirmed environment discovery detects all four new MQTT observer targets.

Build validation:

pio run -e heltec_tracker_v1_1_repeater_observer_mqtt
pio run -e heltec_tracker_v2_repeater_observer_mqtt
pio run -e heltec_tracker_v1_1_room_server_observer_mqtt
pio run -e heltec_tracker_v2_room_server_observer_mqtt

All PlatformIO builds completed successfully.

Assessment

The change is low risk and primarily additive. Tracker v1.1 support is implemented using the existing Tracker v2 codebase where possible, while hardware-specific FEM functionality remains isolated to boards that support it.

[yellowcooln]

The Wireless tracker has no PSRAM, so it is limited to 2 mqtt uploads.