chore: add ai agent guidance - #10376

A few comments:

• I'm not sure how much value the available npm command sections add; IME LLMs seem to find those fine.
• We should add something on where we do and don't use the Canadian spellings of things
• I'd like some guidance to keep code changes minimal and prefer small PRs, and especially to avoid verbose infrastructure and tooling implementations and comments in favor of invoking common command line tools. Code is the enemy; it's where bugs live, and the less of it that we have the better.
• Something about us being very skeptical of dependencies, especially direct dependencies
• Don't propagate existing antipatterns in the interest of maintaining consistency
• Prefer fixing root causes rather than creating lists of exceptions or special-casing particular files or implementations
• Accessibility is important to the project; make sure that changes do not introduce regressions, and that new additions work well for screenreader and keyboard users
• Don't use the DOM/class/CSS/transform methods from dom.ts; they exist for backwards compatibility, but vanilla JS should be used for new code. createSvgElement is allowable. DO use aria.ts for all new code.
• Prefer ? or guards vs ! for Typescript null checks
• Don't remove or revert user-added debugging code during a session unless preparing a final commit/PR.
• New tests should be written in Typescript!
• Always take a final pass for opportunities to condense or simplify changes, and ensure that all changes are still needed and relevant, and that comments are accurate.

Thanks, I'll fold those suggestions in.

re: script commands, claude really seems to want them and I do think explicitly telling it to just run the mocha tests in node for quick verification is better because it does often try to run all of npm run test too often when there is no conceivable need to run the generator goldens for example

Sounds good, and yeah agreed on the guidance to just run the node tests most of the time.

ok, added your recs and also added a section on translating plugin strings