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/pages/Settings.tsx

@@ -1,6 +1,6 @@
 /**
  * @file Settings.tsx
- * @description The install-wide settings, as four pages of the Settings nav (`SettingsHub.tsx`): `section="general"` — language —, `section="data"` — total cost, database overview, workspace housekeeping (dry run first, confirm before a real run), import, remote sources, export, this browser's preferences backup, session cleanup (whole days ≥ 1, a dry-run count in its confirm) and the danger zone (typed confirmation) —, `section="about"` — system information — and `section="notifications"` — browser notifications (per-browser, with a reset) and alerts (server-wide). Server info (`/api/settings/info`) is read only by Data and About, refreshed on activity at most every 10 s (Sagi has its own page, `components/settings/PetSettings.tsx`). Appearance is its own page (`components/settings/AppearanceSettings.tsx`); per-tool settings live in that tool's page under `/settings/agents/<id>`.
+ * @description The install-wide settings, as three pages of the Settings nav (`SettingsHub.tsx`): `section="data"` — total cost, database overview, workspace housekeeping (dry run first, confirm before a real run), import, remote sources, export, this browser's preferences backup, session cleanup (whole days ≥ 1, a dry-run count in its confirm) and the danger zone (typed confirmation) —, `section="about"` — system information — and `section="notifications"` — browser notifications (per-browser, with a reset) and alerts (server-wide). Server info (`/api/settings/info`) is read only by Data and About, refreshed on activity at most every 10 s. Language, theme and the pet live on the Appearance page (`components/settings/AppearanceSettings.tsx`); per-tool settings live in that tool's page under `/settings/agents/<id>`.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 /* =============================================================================
@@ -205,12 +205,12 @@ function useCountUp(end: number | null, durationMs = 1000) {
 // ─── Main component ───
 
 export function Settings({
-  section = "general",
+  section = "notifications",
 }: {
   /** Which Settings page this renders (`/settings/<section>`). */
-  section?: "general" | "data" | "about" | "notifications";
+  section?: "data" | "about" | "notifications";
 } = {}) {
-  const { t, i18n } = useTranslation("settings");
+  const { t } = useTranslation("settings");
   // Only Data and About show server info; General and Notifications never read it.
   const needsInfo = section === "data" || section === "about";
   const [loading, setLoading] = useState(needsInfo);
@@ -541,27 +541,6 @@ export function Settings({
         </div>
       )}
 
-      {section === "general" && (
-        <>
-          <SettingsSection 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>
-        </>
-      )}
-
       {section === "notifications" && (
         <>
           <p className="text-xs text-fg-muted">{t("notifications.scopeNote")}</p>