Function parseStanceWithSide

parseStanceWithSide(
stanceWithSide: string,
): { laterality: StanceLaterality; stance: TrigramStance } | null
Parse a combined stance+laterality string into its components.

Korean: 자세 측면 분리

Takes a string in the format "stance_laterality" and returns the individual stance and laterality components.
Parameters
- stanceWithSide: string
  Combined stance string (e.g., "geon_left")
Returns { laterality: StanceLaterality; stance: TrigramStance } | null
Object with stance and laterality, or null if invalid format
Example
```
const result = parseStanceWithSide("geon_left");
// { stance: "geon", laterality: "left" }

const invalid = parseStanceWithSide("invalid");
// null
```
Korean
자세측면분리
- Defined in systems/trigram/types.ts:77