fix(codex): use path.join for auth detail message path

Use path.join instead of string concatenation for the auth.json
fallback path in the detail message, ensuring correct path
separators on Windows.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/adapters/codex-local/src/server/test.ts

@@ -116,7 +116,7 @@ export async function testEnvironment(
         code: "codex_native_auth_present",
         level: "info",
         message: "Codex is authenticated via its own auth configuration.",
-        detail: codexAuth.email ? `Logged in as ${codexAuth.email}.` : `Credentials found in ${codexHome ?? codexHomeDir()}/auth.json.`,
+        detail: codexAuth.email ? `Logged in as ${codexAuth.email}.` : `Credentials found in ${path.join(codexHome ?? codexHomeDir(), "auth.json")}.`,
       });
     } else {
       checks.push({