fix: update basePath validation test for URL round-trip check

The @ character is valid in URL paths, so it should no longer be
rejected. Updated test to match the new URL-based validation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bartlomieju

packages/fresh/tests/basepath_test.tsx

@@ -11,12 +11,8 @@ Deno.test("basePath validation - rejects invalid paths", () => {
     'Invalid basePath: "/ui/". Must not end with "/" except for root path',
   );
 
-  expect(() => new App({ basePath: "/ui@admin" })).toThrow(
-    'Invalid basePath: "/ui@admin". Contains invalid characters',
-  );
-
   expect(() => new App({ basePath: "/ui admin" })).toThrow(
-    'Invalid basePath: "/ui admin". Contains invalid characters',
+    'Invalid basePath: "/ui admin"',
   );
 });