Add support for ALTHRSQ800WRF (Salus UG800 / Altech ecosystem)

[awfvantets]

Setup

Altech-branded Salus system (Altech is a Salus Controls affiliate, sold via CEDEO/Van Marcke in FR/BE/NL):

• Gateway: ALTHUG800 (reports as UG800, coordinator fw 20250609, sw 020280251020)
• 5× ALTHRSQ800WRF wireless zone thermostats on a ducted heat pump (cooling + heating)

Problem

Reads work fine, but all writes were rejected with IT600CommandError: iT600 gateway rejected 'write' command. The library treats any non-FC600 model as an sIT600TH thermostat, but this device family only accepts the sTherS/sComm data classes (like the FC600).

Verified by direct _make_encrypted_request testing on the device

• {"sIT600TH": {"SetHeatingSetpoint_x100": ...}} → rejected
• {"sIT600TH": {"SetHoldType": 7}} → rejected
• {"sTherS": {"SetCoolingSetpoint_x100": 2150}} → accepted, confirmed on the wall unit (target changed to 21.5)
• {"sTherS": {"SetHeatingSetpoint_x100": 2150}} → accepted

Changes

1. Treat ALTHRSQ800WRF like FC600 in the three model checks (preset / mode / temperature writes).
2. Expose HVAC_MODE_OFF in hvac_modes for the sTherS branch and derive it from sComm.HoldType == 7. Without this, HomeKit (via HA's HomeKit Bridge) cannot represent or set the off state.
3. set_climate_device_mode: map HVAC_MODE_OFF → sComm.SetHoldType 7; when switching on, clear the hold (SetHoldType 2) together with sTherS.SetSystemMode. Also fixes a latent bug where the string constant HVAC_MODE_AUTO was written as the SystemMode value instead of the Zigbee enum (1).

Tested

Full round-trip verified on hardware: temperature set, mode changes (cool/off/on), state correctly reflected in HA and Apple Home, heat pump physically responding.

Note: change 2 also gives FC600 users an explicit OFF hvac_mode (previously only available as preset) — consistent with the existing hvac_action/preset logic, but flagging it for review.

[awfvantets]

Added two follow-up fixes found during further testing:

1. hvac_action strings: "heating (idling)" / "cooling (idling)" are not valid HA HVACAction values. HA's HomeKit Bridge drops climate accessories at startup when an entity reports them. Changed both to "idle".

2. RunningState detection: RunningState is a Zigbee bitmap (bit 0 = heat, bit 1 = cool). The FC600 reports 66 and the ALTHRSQ800WRF reports 6 while cooling — both have the cool bit set. Matching on bits instead of exact values covers both device families (and future ones), so hvac_action now correctly reports cooling/heating on the SQ800 series.

All changes verified on hardware (UG800 + 5× ALTHRSQ800WRF): tiles in Apple Home now correctly show off/idle/cooling states.