Trim a detection's polygon when its bounding box is shrunk over it

[mattdawkins]

Problem

Resizing a detection's bounding box leaves its polygon untouched, so shrinking the box past the polygon leaves polygon geometry sticking out beyond the box.

Fix

Box edits now clip any polygon on the detection to the new bounds using a small Sutherland–Hodgman implementation (clipPolygonToBounds in src/utils.ts, no new dependency):

• Polygons crossing the new box edge are trimmed to fit.
• A polygon falling entirely outside the new box is removed.
• Holes are clipped by the same rule; holes left with fewer than 3 points are dropped.
• Clipping happens against the rounded bounds that setFeature stores, so the trimmed polygon is consistent with the persisted box.
• Rotated boxes are exempt: their stored bounds are the unrotated envelope, so an axis-aligned clip would cut the wrong region.

Redundant full-box polygons are dropped

A polygon identical to the detection's bounding box carries no information beyond the box and makes editing harder, so (second commit):

• When a box shrink clips a polygon down to exactly the new box, the polygon is removed rather than kept as a redundant rectangle.
• On load, Track.fromJSON drops any polygon equal to its feature's bounds (extra collinear vertices and either winding still count as equal; polygons with holes or any interior structure are kept, and other geometry like head/tail points is untouched).

The equality test (polygonEqualsBounds) requires a hole-free polygon whose extent matches the bounds and whose area fills the box — a simple polygon with the area of its bounding box must be that rectangle.

Unit tests cover containment, single/multi-edge clipping, slanted-edge intersection points, full removal, hole handling, box-equality detection (including clip artifacts and near-miss shapes), and the load-time cleanup.

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