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/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