Complete client UI i18n migration

Adds client-side i18n support, language settings, translated UI copy, and locale parity coverage.

packages/app/src/git/policy.test.ts

@@ -1,5 +1,6 @@
-import { describe, expect, it } from "vitest";
+import { afterEach, describe, expect, it } from "vitest";
 import { CheckoutPrStatusSchema } from "@getpaseo/protocol/messages";
+import { i18n } from "@/i18n/i18next";
 
 import { buildGitActions, type BuildGitActionsInput } from "./policy";
 
@@ -132,6 +133,10 @@ function createInput(overrides: Partial<BuildGitActionsInput> = {}): BuildGitAct
 }
 
 describe("git-actions-policy", () => {
+  afterEach(async () => {
+    await i18n.changeLanguage("en");
+  });
+
   it("shows only remote sync actions on the base branch", () => {
     const actions = buildGitActions(createInput({ hasRemote: true }));
 
@@ -599,6 +604,29 @@ describe("git-actions-policy", () => {
     expect(action).toMatchObject({ label: "Merge locally" });
   });
 
+  it("uses the active language for policy-owned action labels and unavailable messages", async () => {
+    await i18n.changeLanguage("zh-CN");
+    const actions = buildGitActions(
+      createInput({
+        hasRemote: true,
+        behindOfOrigin: 1,
+        isOnBaseBranch: false,
+        aheadCount: 0,
+      }),
+    );
+
+    expect(actions.primary).toMatchObject({
+      id: "pull",
+      label: "Pull",
+      pendingLabel: "正在 pull...",
+      successLabel: "已 pull",
+    });
+    expect(actions.secondary.find((entry) => entry.id === "pr")).toMatchObject({
+      label: "创建 PR",
+      unavailableMessage: "无法创建 PR，因为此分支还没有新的 commit",
+    });
+  });
+
   it.each([
     ["draft", { pullRequestIsDraft: true }],
     ["merged", { pullRequestIsMerged: true }],