Use rendered path geometry for curved mark interaction

[gillkyle]

Problem

Curved marks look smooth, but hover selection currently tests the straight polygon connecting their original data points.

In a curved stacked-area chart, the cursor can be visibly inside the top layer while the tooltip selects the layer underneath it.

This PR makes hover selection follow the curve that was actually drawn.

Approach

• Store the rendered path on the final scene mark.
• Use that same path for SVG, Canvas, React Native, and hover selection.
• Keep the existing selection rules: painted shape first, then paint order, then the mark's normal x/y fallback.

Built-in D3 curves get this automatically. Custom marks can use scenePath.

Cost

Every row below is a TanStack Charts bundle or consumer:

TanStack bundle	Gzip change
Browser chart runtime	+292 B
React line-chart consumer	+312 B
Standalone hover resolver	+270 B
Core entry without path interaction	0 B
TanStack curved-line example using a D3 curve	−674 B

The last row shrinks because our old adapter bundled D3's full line and area generators. The new recorder calls the D3 curve function directly, allowing those larger generators to tree-shake out. This is a TanStack implementation saving, not a comparison against D3.

Curved selection is about 0.3 µs slower per query (3.6 vs 3.3 µs). Point-only selection is unchanged. bundle:check remains red because the standalone resolver is 227 B over its existing 2 KiB budget; this draft leaves that trade-off visible for review.

Validated with 775 tests, typecheck, package/docs checks, production build, benchmarks, and live SVG/Canvas checks.

Not included: frame-by-frame animated picking or parsing arbitrary SVG path strings.

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