Function findSolarTermOnDate

24 solar terms (二十四节气) calculation and naming. Odd-numbered terms are 节气 (minor), even-numbered are 中气 (major).

findSolarTermOnDate(
    config: CalendarConfig,
    year: number,
    month: number,
    day: number,
    locale?: string,
): string | null
Find which solar term a Gregorian date falls on (if any)

Checks all 24 solar terms for the given year and adjacent years to determine if the specified date coincides with a solar term day.
Parameters
- config: CalendarConfig
  Calendar configuration
- year: number
  Gregorian year
- month: number
  Month (1-12)
- day: number
  Day of month
- locale: string = 'zh-CN'
  Locale for naming (default: 'zh-CN')
Returns string | null
Solar term name if the date is a solar term day, otherwise null
Example
```
findSolarTermOnDate(CHINESE_CONFIG, 2024, 4, 4, 'zh-CN')   // "清明"
findSolarTermOnDate(CHINESE_CONFIG, 2024, 4, 4, 'zh-TW')   // "清明"
findSolarTermOnDate(CHINESE_CONFIG, 2024, 6, 5, 'zh-CN')   // "芒种"
findSolarTermOnDate(CHINESE_CONFIG, 2024, 6, 5, 'zh-HK')   // "芒種"
findSolarTermOnDate(CHINESE_CONFIG, 2024, 6, 15, 'zh-CN')  // null
```
- Defined in solar-term.ts:273