Function save

save(key: string, data: any): boolean
Save data to localStorage under a namespaced key.
Parameters
- key: string
  Storage key (automatically prefixed with "sg_")
- data: any
  Any JSON-serializable data to save
Returns boolean
True if the save succeeded, false if storage is full or unavailable
Example
```
sg.save('highscore', { score: 9999, name: 'Player1' });
```
- Defined in persistence.ts:11