0.24.1 - variable references opt-in, docs and diagrams

[0.24.1] - 2026-09-15

Variable references are opt-in: {{ is ordinary text without variables (engine#151)

0.24.0 scanned every exercise for {{name}} references and reserved double
braces from schema 1.14 on. Re-pinning the content repos showed why that was
wrong: alc-technology's Ansible course teaches Jinja2, and {{ server }} in
a prompt, an accepted answer or a matching pair is the lesson, not a
variable. The claim in the 0.24.0 notes that no known content used double
braces was not checked against the content repos before publishing. Now
only an exercise that declares variables is scanned; without it, braces
are plain text and no E-VAR-* rule fires. Schema text corrected, version
stays 1.14 (no field changed). README no longer lists parametric exercises
as uncovered. Eight mermaid diagrams (tier model, gap map, parametric
flow, extension lifecycle, Bloom mapping, variables graph, portability
contract, engine/consumer seam) join the docs, rendered on the Pages site.