chore: fix .gitignore — replace blanket *.js exclusion with **/dist/

[PaulGrimshaw]

Problem

.gitignore currently contains:

*.js
*.d.ts
*.d.ts.map
*.js.map

This excludes all .js and .d.ts files globally, which means built output in dist/ is correctly ignored — but so are any legitimate .js config files at the repo root (e.g. eslint.config.mjs would be caught if it were .js). It's also confusing for contributors who run a build and see a wall of 'untracked/ignored' noise.

Fix

Replace with targeted exclusions:

**/dist/

This cleanly ignores build output while leaving root-level .js config files visible.