enable token usage by default (#2841)

frontend/src/content/en/harness/middlewares.mdx

@@ -110,7 +110,7 @@ Tracks LLM token consumption per model call and logs it at the `info` level. Use
 
 ```yaml
 token_usage:
-  enabled: false
+  enabled: true
 ```
 
 ---

frontend/src/content/zh/harness/middlewares.mdx

@@ -110,7 +110,7 @@ title:
 
 ```yaml
 token_usage:
-  enabled: false
+  enabled: true
 ```
 
 ---

frontend/tests/unit/core/settings/local.test.ts

@@ -0,0 +1,10 @@
+import { expect, test } from "vitest";
+
+import { DEFAULT_LOCAL_SETTINGS } from "@/core/settings/local";
+
+test("defaults token usage to header total plus per-turn breakdown", () => {
+  expect(DEFAULT_LOCAL_SETTINGS.tokenUsage).toEqual({
+    headerTotal: true,
+    inlineMode: "per_turn",
+  });
+});