fix(auth): restore unconditional Better-Auth fallback, add unknown-path test

Remove startsWith('/auth') guard that caused non-auth paths to hang with
no response. Better-Auth already handles /health and /auth/health are
explicitly short-circuited before the handler. Add test asserting unknown
paths receive a terminal response within 1s.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

auth/src/index.ts

@@ -28,11 +28,8 @@ const server = createServer(async (req, res) => {
     return;
   }
 
-  // All /auth/* routes handled by Better-Auth
-  if (req.url?.startsWith("/auth")) {
-    await handler(req, res);
-    return;
-  }
+  // All other routes handled by Better-Auth (returns 404 for unknown paths)
+  await handler(req, res);
 });
 
 server.listen(port, "0.0.0.0", () => {