[Bug] Align pointer events with Two.js coordinates and scene order

[jonobr1]

Summary

Follow up on the event system introduced in #16 and align pointer coordinates, hit ordering, bubbling, and missed-event behavior with the actual Two.js scene graph.

Known correctness gaps

• Hit testing uses top-left Two.js world coordinates, while TwoEvent.point subtracts half the canvas width and height and reports a different coordinate space.
• Shapes under different parent groups fall back to event-registration order rather than complete scene-graph draw order.
• A Group with handlers but no registered interactive child is tested through the Group bounding rectangle, which can report hits in empty areas.
• onPointerMissed currently fires on a missed pointer-up; its relationship to click, pointer-down, and pointer-capture semantics is not defined.
• Pointer capture is inferred from the renderer DOM element, but the synthetic Two.js event does not expose a clear capture API.

Two.js now has contains(...) and Group.getShapesAtPoint(...); the React event layer should use the upstream traversal where possible rather than maintain a competing partial ordering model.

Acceptance criteria

• Define and document whether event points are renderer, world, parent-local, or target-local coordinates.
• Return coordinates consistently for click, wheel, pointer, bubbling, and captured events.
• Resolve topmost targets from the complete current Two.js scene order, including nested and reordered groups.
• Define and test Group hit behavior for sparse, nested, transparent, invisible, clipped, and masked content.
• Define onPointerMissed semantics and test down/up/click/cancel sequences.
• Provide a supported pointer-capture pattern for shape dragging.
• Keep bubbling and stopPropagation() behavior deterministic.
• Add renderer coverage for SVG, Canvas, and WebGL where behavior differs.
• Add tests that assert handler calls and event payloads, not only that the renderer element exists.

Related work

• Follow-up to Feature Request: Add event handlers with hit testing from latest dev branch of Two.js #16.
• Scene ordering should remain consistent with [Parity] Reconcile the Two.js scene graph with React updates #29.
• Mask-aware interaction relates to Feature Request: Add useClipMask hook for declarative clipping masks #9.

[jonobr1]

Foundation Update from #29

The scene ordering prerequisite for this issue is now in place via #36 (fixing #29):

• JSX sibling order is strictly reconciled to parent.children in document order during layout effects.
• Direct mutations and sorts set parent._flagOrder = true, signaling to Two.js that draw order and pointer-event hit testing order should be updated.
• Re-ordering and reparenting now work across component trees and across React.memo boundaries via ChildSlotContext.

This unblocks resolving topmost targets and hit testing directly against the authoritative Two.js scene graph (Group.getShapesAtPoint(...) / parent.children).