fix(build): normalize Windows paths in export validation

Normalize path separators to forward slashes before checking if path starts with 'external/' to fix Windows build failures.

Author: jdalton

scripts/validate-dist-exports.mjs

@@ -43,7 +43,9 @@ function checkExport(filePath) {
   // Skip external packages - they are internal implementation details
   // used by public dist/* modules. We only validate public exports.
   const relativePath = path.relative(distDir, filePath)
-  if (relativePath.startsWith('external/')) {
+  // Normalize path for cross-platform compatibility (Windows uses backslashes)
+  const normalizedPath = relativePath.split(path.sep).join('/')
+  if (normalizedPath.startsWith('external/')) {
     return { path: filePath, ok: true, skipped: true }
   }