fix(nitro): Use forward slashes for resolved plugin paths on Windows

`createResolver` returned `node:path` results, so on Windows the server
plugin was registered as `C:\Users\...\runtime\plugins\server`. Nitro
writes plugin paths verbatim into the generated `#nitro/virtual/plugins`
module (`import _x from "<path>"`), where the backslashes are read as
escape sequences, so the import becomes `C:Users...` and both `vite dev`
and `vite build` fail with ERR_MODULE_NOT_FOUND / "failed to resolve
import". Nitro's own plugin paths come from `pathe` and are unaffected.

Normalize the resolved path to forward slashes, which resolve on every
platform.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: dasilvaluis

packages/nitro/src/utils/resolver.ts

@@ -20,6 +20,9 @@ export function createResolver(base: string): Resolver {
   }
 
   return {
-    resolve: (...path) => resolve(resolvedBase, ...path),
+    // Nitro writes plugin paths verbatim into a generated `import "…"` statement, where the
+    // backslashes of a Windows path read as escape sequences (`C:\Users` becomes `C:Users`).
+    // Forward slashes resolve on every platform, so normalize to them.
+    resolve: (...path) => resolve(resolvedBase, ...path).replace(/\\/g, '/'),
   };
 }

packages/nitro/test/resolver.test.ts

@@ -0,0 +1,16 @@
+import { describe, expect, it } from 'vitest';
+import { createResolver } from '../src/utils/resolver';
+
+describe('createResolver', () => {
+  it('resolves relative to the directory of a file URL', () => {
+    const resolver = createResolver(import.meta.url);
+
+    expect(resolver.resolve('../src/utils/resolver.ts')).toMatch(/packages\/nitro\/src\/utils\/resolver\.ts$/);
+  });
+
+  it('never returns backslashes, so the path survives being written into an import string', () => {
+    const resolver = createResolver(import.meta.url);
+
+    expect(resolver.resolve('../runtime/plugins/server')).not.toContain('\\');
+  });
+});