A seed names a design edge and asks for a number of divisions or a target
length, optionally graded geometrically toward the start, the end or both
ends, kept exactly, as a minimum or as a free goal. Seeds are saved with the
model; Seed::spacing gives the node positions meshers and the viewport share.
Part of #230.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo
