Choreograph: unify fx/fxbetween into single smart fx command

- Single !choreograph fx command replaces both fx and fxbetween
- Auto-detects spawnFx vs spawnFxBetweenPoints: two points = between, one = point
- Three strict modes: coordinate (numeric args), token ID (non-numeric), selected (no args)
- Custom FX resolved by ID (starts with -) or name lookup
- Remove fxbetween command entirely
- Update tutorials, header, ScriptKit registration, README, script.json