feat(companion): add experimental usb_tcp envs for six more boards

[Elektr0Vodka]

What

Adds the meshcomod multi-transport companion (*_companion_radio_usb_tcp: USB + TCP + WebSocket + BLE, SNMP agent, manifest OTA) for six more boards and puts them in MESHCOMOD_COMPANION_ENVS, so the companion workflow builds and releases them:

Board	Env	Display
Heltec Wireless Tracker V2	heltec_tracker_v2_companion_radio_usb_tcp	ST7735 TFT
Heltec Vision Master E213	Heltec_E213_companion_radio_usb_tcp	E213 e-ink
Seeed Xiao S3 (Wio-SX1262 kit)	Xiao_S3_companion_radio_usb_tcp	optional SSD1306 OLED
RAK3112	RAK_3112_companion_radio_usb_tcp	none
LilyGo T-ETH Elite	LilyGo_TETH_Elite_sx1262_companion_radio_usb_tcp	none
LilyGo T-Beam S3 Supreme	T_Beam_S3_Supreme_SX1262_companion_radio_usb_tcp	SH1106 OLED

All six are marked experimental in the README, which explains what has not been checked on them.

Why

These are the boards that can take the meshcomod stack without losing anything:

• ESP32-S3: HTTPS OTA needs internal RAM with BLE and Wi-Fi up (see docs/COMPANION_OTA_MEMORY_ROOT_CAUSE.md). Classic ESP32 and C3 have less; C6 needs Arduino core 3.x, which the pinned NimBLE 1.4.3 does not support.
• At least 8 MB flash on the board's existing partition table, so two app slots hold the ~1.6 MB image. No partition changes in this PR.
• The display driver of the board's stock companion builds is reused (or headless, like the WSL3).

Each env is the board's stock BLE companion env plus the same meshcomod block as the V3 and Wireless Tracker usb_tcp envs. BLE_DEBUG_LOGGING is left out because Serial carries the companion protocol in these builds. The T-ETH Elite build runs over Wi-Fi; upstream has no Ethernet companion for it either, so nothing is lost there.

Not included, with reasons: the Station G2/G3 and T-Beam 1W need a default_16MB.csv partition change, the E290, W12 and RC32 use display drivers not yet used in a usb_tcp build, and the 4 MB boards (T3S3, EoRa-S3, ThinkNode M2/M5) would only fit with min_spiffs.csv and a 128 KB filesystem.

How it was tested

• pio run for all six envs: 6 succeeded, no warnings. Flash 1.52 to 1.68 MB, static RAM 150 to 165 KB; per-env sizes in docs/companion_snmp.md.
• bash build.sh get-meshcomod-companion-firmwares-to-build lists all six, so the release matrix picks them up.
• Not tested on hardware: nobody working on the fork owns these boards.

Firmware and build impact

• Six new release images per companion release (CI runtime grows by six parallel runners).
• No change to existing envs, shared code or partition tables.
• The PR build check still only builds V3, V4 and V4 TFT touch; these envs are first built in CI by the companion release workflow.
• The Wireless Tracker V2 has the highest static RAM (165 KB) and no PSRAM, so it is the first board to check for free heap on hardware.

Docs: README device table and fork features row, changelog_ev.md, docs/CI_RELEASES.md, docs/companion_snmp.md.