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/usePets.ts

@@ -1,6 +1,6 @@
 /**
  * @file usePets — the pet list and its actions, shared by the mascot's
- * right-click menu (`PetMenu.tsx`) and Settings → Pet (`settings/PetSettings`):
+ * right-click menu (`PetMenu.tsx`) and Settings → Appearance (`settings/PetSettings`):
  * `GET /api/pets`, wearing a pet (a viewer preference, `prefs.ts`), installing
  * a featured pet (downloaded on its first pick), uploading an image or a
  * `.codex-pet.zip` (worn at once), and deleting your own after a confirm