chore(deps): bump @projectwallace/css-parser to ~0.18.1 (#234)

## Summary

- Bumps `@projectwallace/css-parser` from `~0.17.0` to `~0.18.1`.
- Split out from the at-rule prelude structured-parsing rework (#230) so
the dependency bump can be reviewed independently.
- 0.18.0 added deep parsing of at-rule prelude values
(`calc()`/`env()`/etc. no longer silently dropped from
`MediaFeature`/`SupportsDeclaration` values); 0.18.1 fixed `@supports
selector()` and the `only`/`not` media-query prefix being dropped.
- None of this is used by format-css's current (regex-based) at-rule
prelude formatter, so the bump alone is a no-op for existing behavior —
#230 is what actually takes advantage of it.

## Test plan

- [x] `npx tsc --noEmit`, `npx vitest run`, `npx oxlint`, `npx oxfmt
--check` all clean at the new version, with zero code changes


---
_Generated by [Claude
Code](https://claude.ai/code/session_01AG67iFrhdQAGoTNnC7gmw4)_

Co-authored-by: Claude <noreply@anthropic.com>

Author: bartveneman

package.json

@@ -44,7 +44,7 @@
 		"lint": "oxlint && oxfmt --check"
 	},
 	"dependencies": {
-		"@projectwallace/css-parser": "~0.17.0"
+		"@projectwallace/css-parser": "~0.18.1"
 	},
 	"devDependencies": {
 		"@projectwallace/preset-oxlint": "^0.0.11",