Add vl_link_status package

[chargedup3d]

Bring-up and status package for the VL Link board (ESP32-C3 + SIMCom SIM7070G).

What it does

• Enables the CAN transceiver. hw_init() for this board is empty, so GPIO 6 sits in standby at boot and a CAN scan finds only the local device with no bus errors to explain it.
• Reports LTE state — carrier, SIM, network attach, signal — and mirrors CAN and LTE status on the two onboard LEDs.
• Logs to SD using the firmware's own log subsystem, so files open directly in VESC Tool's log analysis page. The Logs tab can pull a file off the card, which is the only way to get one on mobile.
• Optional SMS control, trip metering, and a movement alert. Sender numbers are only caller ID and therefore forgeable, so the command set can only ever remove capability from the vehicle, never grant it — there is no command that applies throttle, releases a brake or raises a limit.
• Optional remote lock. The Link sends (lock) / (unlock) over can-cmd and the ESC package latches app-disable-output -1; every request is confirmed by a (lock-ack) callback and resent until it lands, and an ack older than 15 s is treated as unknown. This requires a package on the ESC providing (lock), (unlock) and (lock-report id).
• Optional MQTT telemetry over LTE. Off by default; host, port, credentials, client id and topic all configurable and stored in EEPROM. Plain TCP — the SIM7070G's TLS stack is not reachable through the SM* command set.

Hardware-gated in pkgdesc.qml to hwType == "custom module" and hwName == "vl link" — it drives GPIO 6/7/8 and the SIM7070G UART, none of which exist elsewhere.

Uses const memory and the image system. Lisp data is 84604 / 131072 bytes.

Usage is in the package README, including the settings table and a section on diagnosing MQTT.

Lightly tested: SMS and MQTT share the modem thread, and a connect attempt can block it up to 30 s. I haven't run both enabled for long.

[chargedup3d]

Pushed the stack changes from your review — all threads are down to 200 and everything still runs. They'd been inflated while chasing a modem issue and I never walked them back.

Also rewrote the telemetry JSON builder to append one field at a time instead of nesting str-merge, which was the only thing plausibly wanting more than 200 on the modem thread.