Introduces NAMED_CANVAS_PRESETS with id/label/aspectRatio/projectType metadata so the UI can show meaningful preset names (e.g. "YouTube Shorts (1080×1920)") and so downstream code can resolve a preset by intent rather than dimensions.
- NAMED_CANVAS_PRESETS: landscape 16:9, YouTube Shorts 9:16, square, landscape 4:3
- SHORTS_CANVAS_PRESET convenience export for 9:16 vertical
- DEFAULT_CANVAS_PRESETS preserved (derived from NAMED) so existing editor-store consumers keep working
- Unit tests verify shape, ordering, and back-compat derivation