A Point Curve dropdown under the curve graph shows the preset the photo's
point curves match (or Custom) and lists our own built-ins (Linear, Medium
Contrast, Strong Contrast: symmetric S-curves, values chosen here) and the
user's presets; Save Point Curve... names and stores the current four
channels, right-click deletes, Import/Export Presets... read and write
.lccurve JSON files. Presets set only the point curves (parametric curve and
Refine Saturation stay) and are saved with the library preferences.
Engine commands: curve.presets, curve.applyPreset, curve.savePreset,
curve.deletePreset, curve.importPresets, curve.exportPresets; UI commands
file.importCurvePresets / file.exportCurvePresets (file dialogs on desktop).
Fixes#14
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>