A new user guide page, Equation curves, under Sketching: the first curve step by step, Explicit and
Parametric explained with tables of rules to type (a line, a parabola, a wave, a circle, a spiral),
radians, parameters with the involute of a base circle, building a part (a closed flower curve
extruded), editing, and common mistakes. The technical details stay in a short section for scripts
and agents.
Seven pictures, rendered by `cargo xtask book` from new scripts in docs/book/scripts/equation-*.json
(gitignored output, attributed in attribution/pending/docs-equation-curves.md). The Sketching page
keeps a short summary and links to the new page.
Ahmad Khan