Fix invalid device_class + unit_of_measurement combinations for HA 2026.5 (#32)

HA 2026.5 enforces strict validation of device_class/unit_of_measurement
pairs in MQTT discovery payloads. Four categories were broken:

- power_factor: unit was sent as "power_factor" (the FIMP field name); HA
  requires the field to be omitted or empty for this device class. Fixed by
  normalising the display unit separately from the FIMP data-path key.

- illuminance: unit "Lux" is rejected; normalise to "lx". When a sensor
  reports luminance as "%" (some Z-Wave devices), the illuminance device
  class is dropped so the entity becomes a generic sensor rather than
  triggering a validation error.

- reactive_power (regular/export meter): unit "VAr" is rejected; HA requires
  lowercase "var".

- reactive_power (extended meter values, e.g. p_import_react): the unit
  determination logic fell through to the generic power branch and sent "W";
  reactive power extended values now emit "var", apparent power values emit
  "VA", and reactive energy values emit "kvarh".

Fixes #31

Co-authored-by: Claude <noreply@anthropic.com>

futurehome/src/services/_sensor_numeric.ts

@@ -72,12 +72,15 @@ export function _sensor_numeric__components(
 
   if (!data) return undefined;
 
-  const device_class = data[0];
+  let device_class = data[0];
   const name = data[1];
   let unit = svc.props?.sup_units?.[0] ?? data[2];
   if (unit === 'C') unit = '°C';
   if (unit === 'F') unit = '°F';
   if (unit === 'kph') unit = 'km/h';
+  if (unit === 'Lux') unit = 'lx';
+  // HA rejects illuminance + %; drop device_class for percentage-reporting sensors
+  if (device_class === 'illuminance' && unit === '%') device_class = undefined;
   const state_class = data[3];
 
   return {