Add lengthen_ellipse() that approximates the arc length via 128-point
numerical integration, then bisects to find the new angular span matching
the requested delta/total/percent, and adjusts the nearer endpoint.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Options via text input after entity pick:
DE <delta> — extend by delta (negative trims)
TO <total> — set absolute total length / arc length
P <percent> — scale by percentage
<number> — plain number treated as DE delta
Closest end to pick point is modified. Uses CmdResult::LengthenEntity.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>