chore: migrate to oxfmt

[B4nan]

Summary

Replaces Prettier with oxfmt, matching the toolchain in apify-storage-local-js, apify-shared-js, apify-core, apify-web, and crawlee v4.

Stacked on top of #276 (eslint→oxlint migration). Will be retargeted to `master` once the parent merges.

Commits

• `chore: add oxfmt tooling` — adds `oxfmt@0.46.0` devDep, `.oxfmtrc.json` (4-space tabs, single quotes, 120 col), swaps `format` / `format:check` and lint-staged to oxfmt, drops `prettier` and its config files
• `chore: apply oxfmt formatting` — pure `oxfmt --write` reformat across 48 files
• `ci: rename ESLint/Prettier steps to Lint/Format check` — cosmetic CI tweak

Test plan

• `pnpm lint` — clean
• `pnpm format:check` — clean
• `pnpm build` — all 8 turbo tasks succeed

Follow-up

Once this lands, add the reformat commit SHA to `.git-blame-ignore-revs` so blame skips it.