Add eslint-plugin-compat

Editor assessment

The subject states the addition — the `eslint-plugin-compat` plugin is added — which is fully understandable, and the body's squash-merge bullet list adds the genuinely relevant companions: browserslist configuration updates and lint-rule adjustments for demos, showing the plugin was actually wired into the setup (despite the typo `dd` in the first bullet). Type `chore` is accurate for tooling configuration; absent scope is tolerable. Footers are absent. Style is otherwise clean — no trailing period, no junk. The message conveys what was added and how it was integrated, which is sufficient substance for a publishable tooling example.