Add T-Deck Max hardware model

[h3lix1]

Summary

Add T_DECK_MAX = 139 to the shared HardwareModel enum.

Why this is necessary

Firmware needs a stable hardware model ID before the T-Deck Max variant can be represented correctly in device info, clients, and generated firmware headers. The current protobuf master branch already uses 137 for SEEED_WIO_TRACKER_L2 and 138 for CROWPANEL_P4, so T-Deck Max takes the next open value: 139.

What changed

• Adds a single HardwareModel enum value:
  • T_DECK_MAX = 139
• Includes a short comment describing the board as a LILYGO ESP32-S3 handheld with e-paper display and SX1262 radio.

Tests

• trunk fmt protobufs/meshtastic/mesh.proto from the firmware checkout. No applicable linter was configured for this path.
• git -C protobufs diff --check

Reviewer notes

This PR intentionally only reserves the protobuf ID. Firmware support should follow in a separate firmware PR after this protobuf entry is available for generated outputs and the firmware submodule pointer.