build: switch to oxfmt and oxlint

[TheGreatAxios]

Closes CL-9369

Summary

• Remove Prettier and ESLint (prettier, eslint, @eslint/js, typescript-eslint, jiti) with .prettierrc.json, .prettierignore and eslint.config.ts
• Add oxfmt and oxlint as exact-pinned devDependencies; check (run by CI) already calls lint and format:check
• Fix unicorn/no-useless-fallback-in-spread in src/hub/refresh.ts
• .oxfmtrc.json sets printWidth: 80 (Prettier's width); everything else is oxfmt's defaults, including sorting package.json keys
• .oxlintrc.json turns the correctness category from warn to error; no rules are disabled
• lint runs oxlint, format runs oxfmt, format:check runs oxfmt --check

Commits

1. build: switch to oxfmt and oxlint: tooling, configs and lint fixes
2. style: format with oxfmt: mechanical reformat only (1 file changed, 19 insertions(+), 19 deletions(-)), safe to skip in review

Conflicts

None. This PR sits at the top of the open stack, and the format commit covers the whole tree at that tip.