v1.1.15 — Cube drag-to-orbit + edge/corner targets

Follow-up to #60: the navigation cube is now drag-to-orbit (grab-and-spin); a non-moving press still snaps to the tapped face/edge/corner. Faces draw a 3x3 grid so edge/corner zones are discoverable, and the cube is larger (96pt) so they're reachable. Classifier round-trip verified under the iso rotation. 142 tests. Lives here (shared viewport widget) for ecosystem commonality.