Function ganChar

Heavenly Stems (天干) and Earthly Branches (地支) calculations. Used for year/month/day pillars in traditional Chinese timekeeping.

ganChar(index: number): string
Get a Heavenly Stem (天干) character by index
Parameters
- index: number
  Stem index (0-9), wraps around for out-of-range values
Returns string
The corresponding Chinese character
Example
```
ganChar(0)  // "甲"
ganChar(9)  // "癸"
```
- Defined in ganzhi.ts:148