Full rewrite of EN/ZH/JA as a progressive essay with harness-essay spine,
six-pattern toolbox, neighbor comparisons, and SVG-first figures
(dynamic-vs-static, primitives, six patterns). Keep null-isolation and
longest-prefix resume in the teaching runtime; bump translation-sync to v15.
Co-authored-by: Xinlu Lai <CrazyBoyM@users.noreply.github.com>
