Default HUD language to English; Chinese remains switchable

New installs and missing language fall back to en. Settings menu lists
English first; grok-hud lang zh|tw still switches to Chinese variants.

tests/i18n.test.ts

@@ -13,7 +13,8 @@ import type { SessionSnapshot } from "../src/types.js";
 
 describe("i18n + settings language", () => {
   it("defaults and normalizes languages", () => {
-    assert.equal(normalizeLang(undefined), "zh-Hans");
+    assert.equal(normalizeLang(undefined), "en");
+    assert.equal(normalizeLang(""), "en");
     assert.equal(normalizeLang("zh"), "zh-Hans");
     assert.equal(normalizeLang("en"), "en");
     assert.equal(normalizeLang("tw"), "zh-Hant");

tests/layout.test.ts

@@ -106,9 +106,9 @@ describe("layout", () => {
     for (const ln of narrow) {
       assert.ok(visibleLen(ln) <= 50, `line too long: ${visibleLen(ln)} ${stripTmuxStyles(ln)}`);
     }
-    // hierarchy styles present on wide (default language 中文 labels)
+    // hierarchy styles present on wide (default language English labels)
     const joined = wide.join("\n");
     assert.match(joined, /italics|dim|bold/);
-    assert.match(joined, /入 |出 |缓 |窗 /);
+    assert.match(joined, /\bi |\bo |\bc |ctx /);
   });
 });