DRV-39: send current temp resolution dynamically

[svc-finitelabs]

Fixes DRV-39

Summary

• send CURRENT_TEMPERATURE_RESOLUTION_C/F dynamically from visual_current_temperature_step
• keep XML defaults as fallback when ESPHome does not provide the field
• reuse a small Celsius delta to Fahrenheit delta helper in the capability path

Testing

• make init
• make build