Add multi-RAT combined sheet generation to KPI health check Excel export with time-based site aggregation, implement time key normalization for hourly/daily granularity with period_start/date_only column detection, build unified sheet merging 2G/3G/LTE/TWAMP KPIs by site_code and time with RAT prefix columns, extract and merge geographic coordinates from all RATs, and fallback to per-RAT sheets when combined generation fails