feat(morph-loader): add twelve more Material 3 expressive shapes

[dennytosp]

Closes #43

Adds 6-sided-cookie, 9-sided-cookie, 12-sided-cookie, sunny, burst, clover-4, clover-8, flower, triangle, diamond, square and gem, taking SHAPES from 7 to 19.

Grey = already shipped, purple = new. Every shape below is rendered through the component's own pipeline (prepareShape → 80-point resample → straight-line polygon), so this is what the loader actually draws:

Notes

Written as SVG paths. prepareShape already accepts either a point list or a path string, and takes the SVG branch through flattenSvgPath. Authoring the new shapes as paths keeps them readable instead of adding ~600 numbers each, and lets Skia flatten them at exactly the resolution the loader samples.

Wound to match. All seven shipped shapes have a negative signed area and start near the top. Morphing interpolates point k of shape A to point k of shape B, so a shape wound the other way collapses through a degenerate midpoint. The new shapes follow the same convention — this was worth getting right, since it is invisible in a static render and only shows up mid-morph.

Defaults are unchanged. defaultShapes used to be Object.values({ ...SHAPES }), so adding any shape would have silently changed what an existing <MorphLoader /> renders. It now reads an explicit DEFAULT_SHAPE_KEYS list holding the original seven in their original order.

Verification

• defaultShapes is byte-identical to main — an existing loader with no shapes prop cycles through exactly what it did before.
• All 342 ordered shape pairs were interpolated at the midpoint: no NaN, and the worst area retention is 82.2% (4-sided-cookie → square). A mis-wound shape shows up here as a near-zero retention.
• All 12 new shapes take the SVG-path branch of prepareShape; the 7 originals still take the point-list branch.
• tsc --noEmit reports the same error count as main (none in these files).

Sample morphs, shipped → new:

Open question

I kept the default rotation at the original seven so nothing changes for existing users. If you would rather the defaults cycle through more of the set, that is a one-line change to DEFAULT_SHAPE_KEYS — happy to adjust.