feat 🥁: add no-unknown-unit rule

Adds a rule to disallow unknown or invalid CSS units in vanilla-extract style objects.

- Reports any usage of unrecognized units in property values
- Handles all vanilla-extract APIs (style, styleVariants, recipe, etc.)
- Ignores valid units in special contexts (e.g., CSS functions, custom properties)

No autofix is provided because replacing or removing unknown units may result in unintended or invalid CSS. Manual developer review is required to ensure correctness.

src/css-rules/no-zero-unit/rule-definition.ts

@@ -12,7 +12,7 @@ const noZeroUnitRule: Rule.RuleModule = {
     fixable: 'code',
     schema: [],
     messages: {
-      noZeroUnit: 'Unit with zero value is unnecessary. Use 0 instead.',
+      noZeroUnit: 'Zero values don’t need a unit. Replace with "0".',
     },
   },
   create(context) {