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/App.tsx

@@ -70,6 +70,7 @@ import { NotFound } from "./pages/NotFound";
 import { useWebSocket } from "./hooks/useWebSocket";
 import { useNotifications } from "./hooks/useNotifications";
 import { eventBus } from "./lib/eventBus";
+import { copyOnCtrlShiftC } from "./lib/keys";
 import type { WSMessage } from "./lib/types";
 
 // The heavy pages (xterm, the diff viewer, the settings editors) load on first
@@ -128,6 +129,12 @@ export default function App() {
     return () => window.removeEventListener("vite:preloadError", onPreloadError);
   }, []);
 
+  // Ctrl+Shift+C is copy here (Linux terminal habit), not the browser's inspector.
+  useEffect(() => {
+    window.addEventListener("keydown", copyOnCtrlShiftC, true);
+    return () => window.removeEventListener("keydown", copyOnCtrlShiftC, true);
+  }, []);
+
   return (
     <>
       <SplashScreen />