Function getSignIndex

getSignIndex(longitude: number): number
Get the sign (0-11) for a given ecliptic longitude.
Parameters
- longitude: number
  Ecliptic longitude in degrees
Returns number
Sign index (0 = Aries, 11 = Pisces)
Example
```
getSignIndex(0)     // 0 (Aries)
getSignIndex(45)    // 1 (Taurus)
getSignIndex(359)   // 11 (Pisces)
```
- Defined in aspects/angular-separation.ts:200