feat: edit in the Changes panel, git graph history, plan quota (v2.3.0)

- Changes panel: a working file opens in a CodeMirror editor with its diff
  inline (DiffEditor.tsx, @codemirror/merge, lazy-loaded); Changes folds the
  unchanged lines, Whole file shows them; side by side at 50/50 and full
  width; a Revert per block; original from HEAD or the branch's merge base
  (`mergeBase` on GET /git/changes?range=branch)
- Every diff: green = line added whole, red = removed whole, blue = edited
  in place (--diff-mod)
- History drawn as a commit graph (#58: `parents` on GET /git/log,
  --date-order; lib/commitGraph.ts)
- Per-workspace never-stage list, drawn orange in the Files tree (--kept);
  closed Terminal rows past three deleted
- Status bar plan quota for Claude (per account) and Codex
  (GET /api/pricing/quota, server/lib/quota.js); compact hover panel that
  stays open, Refresh button with a spinner
- Settings → Appearance holds language, theme and pet; Ctrl+Shift+C copies;
  compact sidebar navigation and short session times

client/src/components/settings/AppearanceSettings.tsx

@@ -1,8 +1,10 @@
 /**
  * @file AppearanceSettings.tsx
- * @description Settings → Appearance (`/settings/appearance`): the Dark / Light / System mode switch and
- * one named-theme picker per mode (state in `hooks/useTheme.ts`, palettes in
- * `index.css`). Each card's swatch re-scopes the theme's CSS variables on its
+ * @description Settings → Appearance (`/settings/appearance`): the interface language, the
+ * Dark / Light / System mode switch and one named-theme picker per mode, and the
+ * corner pet (`PetSettings`, deep-linked as `#pet`) — the old General and Pet
+ * pages redirect here. Theme state is in `hooks/useTheme.ts`, palettes in
+ * `index.css`. Each card's swatch re-scopes the theme's CSS variables on its
  * own element (`dark` class or `data-mode`, plus `data-theme`), so the preview
  * is painted by the same tokens as the app — no hex is duplicated here.
  * **Reset to defaults** (after a confirm) returns to Dark with both stock themes.
@@ -11,7 +13,8 @@
 
 import { useTranslation } from "react-i18next";
 import { Monitor, Moon, RotateCcw, Sun } from "lucide-react";
-import { SettingsRow, SettingsSegmented } from "./SettingsRow";
+import { SettingsRow, SettingsSection, SettingsSegmented } from "./SettingsRow";
+import { PetSettings } from "./PetSettings";
 import { THEMES, useTheme, type Theme, type ThemeMode } from "../../hooks/useTheme";
 import { confirmDialog } from "../../lib/confirm";
 import { toast } from "../../lib/toast";
@@ -61,7 +64,7 @@ function Swatch({ mode, name }: { mode: Theme; name: string }) {
 }
 
 export function AppearanceSettings() {
-  const { t } = useTranslation("settings");
+  const { t, i18n } = useTranslation("settings");
   const { mode, theme, themeFor, setMode, setThemeFor } = useTheme();
 
   const reset = async () => {
@@ -78,67 +81,99 @@ export function AppearanceSettings() {
   };
 
   return (
-    <div className="card p-5 space-y-5">
-      <SettingsRow
-        label={t("appearance.mode")}
-        control={
-          <SettingsSegmented
-            ariaLabel={t("appearance.mode")}
-            value={mode}
-            onChange={setMode}
-            options={MODES.map(({ mode: m, Icon }) => ({
-              value: m,
-              label: (
-                <>
-                  <Icon className="w-3.5 h-3.5" />
-                  {t(`appearance.modes.${m}`)}
-                </>
-              ),
-            }))}
-          />
-        }
-      />
+    <div className="space-y-6">
+      <SettingsSection
+        id="language"
+        title={t("language.title")}
+        description={t("language.description")}
+      >
+        <SettingsRow
+          label={t("language.label")}
+          control={
+            <SettingsSegmented
+              ariaLabel={t("language.label")}
+              value={(i18n.resolvedLanguage ?? i18n.language).startsWith("vi") ? "vi" : "en"}
+              onChange={(v) => void i18n.changeLanguage(v)}
+              options={[
+                { value: "en" as const, label: t("language.names.en") },
+                { value: "vi" as const, label: t("language.names.vi") },
+              ]}
+            />
+          }
+        />
+      </SettingsSection>
 
-      {(["dark", "light"] as const).map((group) => (
-        <div key={group}>
-          <p className="text-xs font-medium text-fg-secondary mb-2">
-            {t(`appearance.${group}Themes`)}
-            {theme === group && (
-              <span className="ml-2 text-fg-muted font-normal">{t("appearance.active")}</span>
-            )}
-          </p>
-          <div className="grid grid-cols-2 sm:grid-cols-3 lg:grid-cols-4 gap-3">
-            {THEMES[group].map((name) => {
-              const selected = themeFor[group] === name;
-              const label = THEME_LABELS[name] ?? t("appearance.default");
-              return (
-                <button
-                  key={name}
-                  type="button"
-                  onClick={() => setThemeFor(group, name)}
-                  aria-pressed={selected}
-                  aria-label={`${t(`appearance.${group}Themes`)}: ${label}`}
-                  className={`rounded-lg border p-1.5 text-left transition-colors ${
-                    selected
-                      ? "border-accent ring-2 ring-accent/40"
-                      : "border-border hover:border-border-light"
-                  }`}
-                >
-                  <Swatch mode={group} name={name} />
-                  <span className="block px-1 pt-1.5 text-xs text-fg-primary">{label}</span>
-                </button>
-              );
-            })}
+      <section id="theme" className="card p-5 space-y-5 scroll-mt-24">
+        <h3 className="text-sm font-semibold text-fg-primary">{t("appearance.theme")}</h3>
+        <SettingsRow
+          label={t("appearance.mode")}
+          control={
+            <SettingsSegmented
+              ariaLabel={t("appearance.mode")}
+              value={mode}
+              onChange={setMode}
+              options={MODES.map(({ mode: m, Icon }) => ({
+                value: m,
+                label: (
+                  <>
+                    <Icon className="w-3.5 h-3.5" />
+                    {t(`appearance.modes.${m}`)}
+                  </>
+                ),
+              }))}
+            />
+          }
+        />
+
+        {(["dark", "light"] as const).map((group) => (
+          <div key={group}>
+            <p className="text-xs font-medium text-fg-secondary mb-2">
+              {t(`appearance.${group}Themes`)}
+              {theme === group && (
+                <span className="ml-2 text-fg-muted font-normal">{t("appearance.active")}</span>
+              )}
+            </p>
+            <div className="grid grid-cols-2 sm:grid-cols-3 lg:grid-cols-4 gap-3">
+              {THEMES[group].map((name) => {
+                const selected = themeFor[group] === name;
+                const label = THEME_LABELS[name] ?? t("appearance.default");
+                return (
+                  <button
+                    key={name}
+                    type="button"
+                    onClick={() => setThemeFor(group, name)}
+                    aria-pressed={selected}
+                    aria-label={`${t(`appearance.${group}Themes`)}: ${label}`}
+                    className={`rounded-lg border p-1.5 text-left transition-colors ${
+                      selected
+                        ? "border-accent ring-2 ring-accent/40"
+                        : "border-border hover:border-border-light"
+                    }`}
+                  >
+                    <Swatch mode={group} name={name} />
+                    <span className="block px-1 pt-1.5 text-xs text-fg-primary">{label}</span>
+                  </button>
+                );
+              })}
+            </div>
           </div>
-        </div>
-      ))}
+        ))}
 
-      <div className="flex justify-end border-t border-border pt-3">
-        <button type="button" onClick={() => void reset()} className="btn-ghost text-xs">
-          <RotateCcw className="w-3.5 h-3.5" />
-          {t("appearance.reset")}
-        </button>
-      </div>
+        <div className="flex justify-end border-t border-border pt-3">
+          <button type="button" onClick={() => void reset()} className="btn-ghost text-xs">
+            <RotateCcw className="w-3.5 h-3.5" />
+            {t("appearance.reset")}
+          </button>
+        </div>
+      </section>
+
+      <section id="pet" className="space-y-3 scroll-mt-24">
+        <div>
+          <h3 className="text-sm font-semibold text-fg-primary">{t("appearance.pet")}</h3>
+          <p className="mt-0.5 text-xs text-fg-muted">{t("appearance.petDescription")}</p>
+        </div>
+        <PetSettings />
+      </section>
     </div>
   );
 }

client/src/components/settings/PetSettings.tsx

@@ -1,5 +1,5 @@
 /**
- * @file PetSettings — Settings → Pet: the mascot's own page. Show it or not,
+ * @file PetSettings — the pet block of Settings → Appearance (`#pet`). Show it or not,
  * its speech bubbles, its size (with a live preview), and which pet it wears
  * from a grid — Sagi, the featured codex-pets.net pets (downloaded into this
  * install on the first pick, never bundled), and your own (deletable) — plus

client/src/components/settings/__tests__/AppearanceSettings.test.tsx

@@ -1,14 +1,17 @@
 /**
  * @file AppearanceSettings.test.tsx
- * @description Tests for the Settings → Appearance section: the mode switch and the per-mode theme cards write through useTheme to `<html>`.
+ * @description Tests for the Settings → Appearance section: the language switch, and the mode switch and the per-mode theme cards writing through useTheme to `<html>`.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
-import { describe, it, expect, beforeEach } from "vitest";
-import { render, screen } from "@testing-library/react";
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { act, render, screen, within } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
+import i18n from "../../../i18n";
 import { AppearanceSettings } from "../AppearanceSettings";
 
+vi.mock("../PetSettings", () => ({ PetSettings: () => <div data-testid="pet-settings" /> }));
+
 const root = document.documentElement;
 
 describe("AppearanceSettings", () => {
@@ -19,6 +22,22 @@ describe("AppearanceSettings", () => {
     root.removeAttribute("data-mode");
   });
 
+  it("switches the interface language and holds the pet block", async () => {
+    const user = userEvent.setup();
+    render(<AppearanceSettings />);
+    expect(screen.getByTestId("pet-settings").closest("section")).toHaveAttribute("id", "pet");
+    const group = screen.getByRole("radiogroup", { name: "Interface language" });
+    expect(within(group).getByRole("radio", { name: "English" })).toHaveAttribute(
+      "aria-checked",
+      "true"
+    );
+    await user.click(within(group).getByRole("radio", { name: "Tiếng Việt" }));
+    expect(i18n.language).toBe("vi");
+    await act(async () => {
+      await i18n.changeLanguage("en");
+    });
+  });
+
   it("renders every theme of both modes, defaults selected", () => {
     render(<AppearanceSettings />);
     const pressed = screen