fix: resolve Sass alias imports via loadPaths instead of absolute paths for Windows compatibility

[Copilot]

Windows CI fails because Sass misinterprets drive letters (C:) in absolute @use paths as URL schemes, producing "Can't find stylesheet to import" errors.

From CI logs:

@use "C:/Users/RUNNER~1/AppData/Local/Temp/.../src/styles/tokens" as *;
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Can't find stylesheet to import.

Change

When resolveAlias matches an import like @/styles/tokens:

• Before: Rewrites to absolute path → @use "C:/Users/.../src/styles/tokens" (breaks on Windows)
• After: Adds alias root to Sass loadPaths and rewrites to relative suffix → @use "styles/tokens"

// New: resolve alias via loadPaths (cross-platform)
const aliasResult = tryResolveViaAlias(impPath)
if (aliasResult) {
  const { suffix, aliasRoot } = aliasResult
  compileOptions.loadPaths.push(aliasRoot)
  return `@${kw} ${quote}${suffix}${quote}`
}

Also extracted duplicated getAliasSuffix helper into a shared function.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>ci windows test failed</issue_title>
<issue_description>ci windows test failed，下面是失败的原因，我猜测可能是windows上一些文件路径的问题

Run nr test

transform-to-unocss@0.1.24-beta.3 test D:\a\transformToUnoCSS\transformToUnoCSS
vitest

RUN v3.2.4 D:/a/transformToUnoCSS/transformToUnoCSS

✓ test/sass-mixed-decls.test.ts (5 tests) 519ms
✓ sassCompiler deprecation warnings fix > should compile SCSS with mixed declarations without warnings 445ms
stdout | test/complex-scss-for-loop.test.ts > Complex SCSS for-loop and variable syntax > should handle SCSS @for loops with variables correctly
Testing complex SCSS with @for loops and variables...
[DEBUG] transformCode started: {"filepath":"complex-scss-test.vue","isJsx":true,"codeLength":3103}
[DEBUG] transformCode detected type: vue, original type: undefined, filepath: complex-scss-test.vue
[DEBUG] transformCode: Processing as Vue file

stdout | test/complex-scss-for-loop.test.ts > Complex SCSS for-loop and variable syntax > should handle SCSS @for loops with variables correctly
[DEBUG] transformVue started: {
"filepath": "complex-scss-test.vue",
"isJsx": true,
"codeLength": 3103
}
[DEBUG] After inline style transformation
[DEBUG] transformMedia: No https://github.com/media queries found

stdout | test/complex-scss-for-loop.test.ts > Complex SCSS for-loop and variable syntax > should handle SCSS @for loops with variables correctly
[DEBUG] Processing styles: {
"stylesCount": 1
}
[transform-to-unocss] Compiling SCSS file: complex-scss-test.vue

stdout | test/complex-scss-for-loop.test.ts > Complex SCSS for-loop and variable syntax > should handle SCSS @for loops with variables correctly
[DEBUG] CSS compiled successfully: {
"styleIndex": 0,
"originalStyleLength": 2221,
"compiledCssLength": 4612,
"scoped": true
}

stdout | test/complex-scss-for-loop.test.ts > Complex SCSS for-loop and variable syntax > should handle SCSS @for loops with variables correctly
[DEBUG] importCss started: {
"filepath": "complex-scss-test.vue",
"styleLength": 4612,
"hasImports": false
}

color: $brand-color;
}
</style>
❯ test/transformAstro.test.ts:57:20
55| })
56|
57| expect(result).toContain('text-red')
| ^
58| expect(result).not.toContain('$brand-color')
59|

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯[1/1]⎯

Test Files 1 failed | 14 passed (15)
Tests 1 failed | 63 passed (64)
Start at 06:43:33
Duration 6.63s (transform 546ms, setup 0ms, collect 6.36s, tests 6.84s, environment 4ms, prepare 2.21s)

Error: AssertionError: expected '---\nexport const prerender = true;\n…' to contain 'text-red'

Expected
Received
text-red
export const prerender = true;
hi

<style> @use "@/styles/tokens" as *; .title { color: $brand-color; } </style>

❯ test/transformAstro.test.ts:57:20

 ELIFECYCLE  Test failed. See above for more details.
Error: Process completed with exit code 1.</issue_description>

<agent_instructions>这个问题没有修复，还是存在</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@Simon-He95 @copilot 问题仍然存在

• Fixes ci windows test failed #68

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