fix: allow Tailwind v4 digit-leading token names

[Bortlesboat]

Summary

• relax the Tailwind v4 token-name validator so names like \2xs\ and \4xl\ can export
• keep rejecting dotted and space-containing token names
• update the Tailwind v4 emitter regression test for digit-leading spacing and radius tokens

Fixes #71.

Verification

• RED: \
  px bun test packages/cli/src/linter/tailwind/v4/handler.test.ts\ failed on the new digit-leading token test before the handler change
• GREEN: \
  px bun test packages/cli/src/linter/tailwind/v4/handler.test.ts\ -> 9 pass, 0 fail
• \
  px bun test packages/cli/src/linter/tailwind/v4\ -> 17 pass, 0 fail
• \git diff --check\

Note

• \./node_modules/.bin/tsc.exe --project packages/cli/tsconfig.build.json --noEmit\ is blocked locally by dependency declaration errors in \�un-types\ under the transient \
  px bun\ install before reaching this change.

[davideast]

Hey @Bortlesboat! Apologies on the delay. I'm going to give this a review here soon.

[davideast]

@Bortlesboat Thank you so much. Looks good. Clean fix, good test update.