Add a lint check that prevents introduction of Unicode emdash (U+2014)
and endash (U+2013) characters. These are almost exclusively introduced
by AI agents and conflict with the project writing style.
The lint script (scripts/check_emdash.sh) checks only added lines in
the current diff by default, so existing violations do not block CI.
Pass --all to scan the entire repo for auditing.
Agent instructions in AGENTS.md, site/AGENTS.md, and the docs style
guide now explicitly ban emdash, endash, and " -- " as punctuation,
with guidance to use commas, semicolons, or periods instead.
Mathias Fredriksson