fix(sorting): sorting custom classnames to the front

[Stybo]

Before:
<div class="p-3 shadow-xl select2-dropdown">

After
<div class="select2-dropdown p-3 shadow-xl">

Closes #22

[sergioazoc]

Thanks for taking the time to send a fix, @Stybo — genuinely appreciated.

I'm going to close this without merging, for three reasons:

1. The behavior is already there in v1.0.0. The sort worker calls ds.getClassOrder() and orders null-order (custom/unknown) classes to the front, matching prettier-plugin-tailwindcss. Verified: p-3 shadow-xl select2-dropdown → select2-dropdown p-3 shadow-xl.
2. The patch targets the pre-v1 tree. v1 reorganized the repo into a pnpm monorepo (packages/oxlint-tailwindcss/src/...) and rewrote the sort path — the heuristic fallback this PR builds on was removed in favor of fail-loud — so it no longer applies cleanly.
3. The per-variant re-sort would diverge from prettier-plugin-tailwindcss, which the worker matches by construction through getClassOrder.

The original #22 divergence turned out to be a stylesheet-config mismatch (oxfmt and the plugin reading different CSS) — details in #22 and the interop guide: https://oxlint-tailwindcss.pages.dev/interop

Thanks again for the contribution and the detailed reports across #22/#23 — they were genuinely useful in tightening the v1 behavior and docs.