Function createEmptyChart

createEmptyChart(
    bpm?: number,
    name?: string,
    options?: Partial<RpeMeta>,
): RpeJson
Create a minimal empty RPE chart with sensible defaults.

The chart has:
- One BPM entry at beat 0
- An empty judgeLineList
- A single 'default' group
- Zero chartTime
Parameters
- bpm: number = 120
  Initial BPM (default: 120).
- name: string = "Untitled"
  Chart name shown in the game (default: 'Untitled').
- options: Partial<RpeMeta> = {}
  Additional metadata fields to override (RpeMeta).
Returns RpeJson
A valid, empty RpeJson ready to populate.
Example
```
const chart = createEmptyChart(140, 'Song Name', {
  charter:  'Me',
  composer: 'Artist',
  level:    'SP Lv.15',
  song:     'song.ogg',
  background: 'bg.png',
});
```
- Defined in chart-utils.ts:156