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/commitGraph.ts

@@ -0,0 +1,76 @@
+/**
+ * @file Lays out the Changes panel's History as a commit graph (the JetBrains /
+ * `git log --graph` shape): each commit gets a column, and each row lists the
+ * line segments drawn through it — a lane passing by, the lanes converging on
+ * the commit from above, and the lines leaving it for its parents below.
+ * Expects the commits in an order where no parent precedes a child
+ * (`git log --date-order`); a parent outside the list leaves its lane running
+ * off the bottom.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+/** One line in a row, in column units; y runs 0 (top) → 0.5 (node) → 1 (bottom). */
+export interface GraphSeg {
+  x1: number;
+  y1: number;
+  x2: number;
+  y2: number;
+  color: number;
+}
+
+export interface GraphRow {
+  col: number;
+  color: number;
+  segs: GraphSeg[];
+}
+
+export function commitGraph(commits: { sha: string; parents: string[] }[]): {
+  rows: GraphRow[];
+  width: number;
+} {
+  // lanes[j] = the sha the lane in column j is waiting for; colors[j] its hue.
+  const lanes: (string | null)[] = [];
+  const colors: number[] = [];
+  const hue = (j: number) => colors[j] ?? 0;
+  let nextColor = 0;
+  let width = 1;
+  const open = () => {
+    const free = lanes.indexOf(null);
+    const j = free < 0 ? lanes.length : free;
+    colors[j] = nextColor++;
+    return j;
+  };
+
+  const rows = commits.map((c) => {
+    const segs: GraphSeg[] = [];
+    let col = lanes.indexOf(c.sha);
+    // A tip nothing above points at: a lane of its own, no line from the top.
+    if (col < 0) {
+      col = open();
+      lanes[col] = null;
+    }
+    lanes.forEach((s, j) => {
+      if (s === null) return;
+      segs.push(
+        s === c.sha
+          ? { x1: j, y1: 0, x2: col, y2: 0.5, color: hue(j) }
+          : { x1: j, y1: 0, x2: j, y2: 1, color: hue(j) }
+      );
+    });
+    const color = hue(col);
+    lanes.forEach((s, j) => {
+      if (s === c.sha) lanes[j] = null;
+    });
+
+    c.parents.forEach((p, i) => {
+      let j = i === 0 ? col : lanes.indexOf(p);
+      if (j < 0) j = open();
+      lanes[j] = p;
+      segs.push({ x1: col, y1: 0.5, x2: j, y2: 1, color: hue(j) });
+    });
+    while (lanes.length && lanes[lanes.length - 1] === null) lanes.pop();
+    width = Math.max(width, lanes.length, col + 1);
+    return { col, color, segs };
+  });
+  return { rows, width };
+}