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/Sagi/PetMenu.tsx

@@ -7,7 +7,7 @@
  * codex-pets.net for more, and open the Sagi settings. The choice and the size
  * are viewer preferences (`prefs.ts`); the pets themselves live on the server
  * (`server/lib/pets.js`); the list and its actions are `usePets`, shared
- * with Settings → Pet.
+ * with Settings → Appearance.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */