Restore card flight animations

[austin-smith]

What Changed

• Moved the drag flight-boundary state (dropAnimationOffset, dragReturnOffset, overlayTilt, isDroppingCards, droppingSelection, isReturningDrag, returningCards, pendingDropDestination, and the waste return anchor) from DragInteractionController back to @State on ContentView — the storage it had before Stop per-frame whole-board re-evaluation #71.
• DragInteractionController now holds only the true per-frame gesture state: dragTranslation and activeTarget.
• DragOverlayView receives the flight-boundary fields as plain values from ContentView and keeps reading only dragTranslation from the controller.

Why

#71 broke every card flight animation: tap-to-move, drag-drop snap, auto-finish, and the invalid-drop return spring all became instant teleports. These flights are driven by withAnimation writes, and an @Observable property loses that transaction when another property has already invalidated the reader in the same tick — the first unanimated write (isDroppingCards = true) stamps the update, and the spring on the offset write behind it is dropped. @State animates per attribute, so the identical write sequence keeps its spring.

None of the shipped performance work is given back: the per-frame drag writes stay isolated in the controller, the moved fields change twice per flight (not per frame) at moments where ContentView already re-evaluates for toolbar enablement, and the board views still prune via their Equatable gates.

Validation

• Bisected with a scripted repro (fixture launch → axe tap/swipe → simctl video → per-frame hash diff): pre-Reduce per-move gameplay lag #70 and Reduce per-move gameplay lag #70 show an ~8-frame flight run, Stop per-frame whole-board re-evaluation #71 and current main show a single-frame teleport.
• Same repro on this branch: tap-to-move flight restored (8-frame run matching the pre-Reduce per-move gameplay lag #70 baseline, mid-flight frame visually confirmed), drag-drop snap and invalid-drop return spring both animate again.
• Full unit suite on macOS: 559 tests, 0 failures.
• macOS and iOS simulator builds succeed.

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