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/__tests__/Pets.test.tsx

@@ -159,7 +159,7 @@ describe("PetMenu", () => {
     fireEvent.click(screen.getByText("Hide pet"));
     expect(sagiPrefs.getEnabled()).toBe(false);
     // Says where to bring it back.
-    expect(toasts.some((x) => /Settings → Pet/.test(x.message))).toBe(true);
+    expect(toasts.some((x) => /Settings → Appearance/.test(x.message))).toBe(true);
     off();
   });