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/lib/__tests__/commitGraph.test.ts

@@ -0,0 +1,48 @@
+/**
+ * @file Tests for the History commit-graph layout: a straight line, a branch
+ * merged back, converging lanes and a parent beyond the loaded page.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+import { describe, it, expect } from "vitest";
+import { commitGraph } from "../commitGraph";
+
+const c = (sha: string, ...parents: string[]) => ({ sha, parents });
+
+describe("commitGraph", () => {
+  it("draws a linear history in one column", () => {
+    const { rows, width } = commitGraph([c("c", "b"), c("b", "a"), c("a")]);
+    expect(width).toBe(1);
+    expect(rows.map((r) => r.col)).toEqual([0, 0, 0]);
+    // The tip has no line from above; the root none below.
+    expect(rows[0]?.segs).toEqual([{ x1: 0, y1: 0.5, x2: 0, y2: 1, color: 0 }]);
+    expect(rows[2]?.segs).toEqual([{ x1: 0, y1: 0, x2: 0, y2: 0.5, color: 0 }]);
+  });
+
+  it("opens a lane for a merged branch and closes it at the fork point", () => {
+    //   m        merge of b2 into a2
+    //   |\\
+    //   a2 b2
+    //   |  b1
+    //   |/
+    //   a1
+    const { rows, width } = commitGraph([
+      c("m", "a2", "b2"),
+      c("a2", "a1"),
+      c("b2", "b1"),
+      c("b1", "a1"),
+      c("a1"),
+    ]);
+    expect(width).toBe(2);
+    expect(rows.map((r) => r.col)).toEqual([0, 0, 1, 1, 0]);
+    expect(rows[0]?.segs).toContainEqual({ x1: 0, y1: 0.5, x2: 1, y2: 1, color: 1 });
+    // b1's lane converges into a1's column.
+    expect(rows[4]?.segs).toContainEqual({ x1: 1, y1: 0, x2: 0, y2: 0.5, color: 1 });
+    expect(rows[1]?.color).toBe(rows[0]?.color);
+    expect(rows[2]?.color).not.toBe(rows[0]?.color);
+  });
+
+  it("keeps a lane running for a parent past the page", () => {
+    const { rows } = commitGraph([c("b", "a")]);
+    expect(rows[0]?.segs).toEqual([{ x1: 0, y1: 0.5, x2: 0, y2: 1, color: 0 }]);
+  });
+});