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

server/lib/git-diff.js

@@ -508,7 +508,7 @@ async function synthesizeAddedPatch(dir, file) {
  *   `file` is set, which is already a full read of one file.
  * @param {number} [opts.context] Unchanged lines around each hunk. The panel
  *   raises this to expand a diff towards the whole file.
- * @returns {Promise<{range, base, baseRef, sha, context, files, truncated}>}
+ * @returns {Promise<{range, base, baseRef, mergeBase, sha, context, files, truncated}>}
  */
 async function collectChanges(
   dir,
@@ -520,11 +520,17 @@ async function collectChanges(
   const ctx = normalizeContext(context);
 
   let baseRef = null;
+  // The commit a branch diff is taken from (`<baseRef>...HEAD`): the editor
+  // reads a file's original text there.
+  let mergeBase = null;
   if (range === "branch") {
     baseRef = await resolveBaseRef(dir, base);
     if (!baseRef) {
       throw badRequest("ENOBASE", "no base branch to compare against");
     }
+    mergeBase = await git(dir, ["merge-base", baseRef, "HEAD"])
+      .then((r) => r.stdout.trim() || null)
+      .catch(() => null);
   }
   if (range === "commit") {
     if (!sha || !SAFE_REV.test(sha)) throw badRequest("EBADREV", "sha is not a valid revision");
@@ -598,7 +604,7 @@ async function collectChanges(
     }
   }
 
-  return { range, base, baseRef, sha, context: ctx, files, truncated };
+  return { range, base, baseRef, mergeBase, sha, context: ctx, files, truncated };
 }
 
 /**
@@ -615,8 +621,10 @@ async function collectChanges(
  */
 async function listCommits(dir, { limit = 30, file = null } = {}) {
   const n = Math.min(Math.max(Number(limit) || 30, 1), 200);
-  const format = ["%H", "%h", "%s", "%an", "%aI", "%D"].join("%x1f");
-  const args = ["log", `-${n}`, `--format=${format}%x1e`];
+  const format = ["%H", "%h", "%s", "%an", "%aI", "%D", "%P"].join("%x1f");
+  // --date-order: no parent before all its children, which the history's
+  // commit graph needs to draw a lane down to each parent.
+  const args = ["log", `-${n}`, "--date-order", `--format=${format}%x1e`];
   // Through the same lexical guard as every other path: in a subdirectory
   // lane `../x` would list commit metadata for a path outside the lane.
   if (file) args.push("--", lanePath(file));
@@ -625,7 +633,7 @@ async function listCommits(dir, { limit = 30, file = null } = {}) {
   for (const record of result.stdout.split("\x1e")) {
     const line = record.replace(/^\n/, "");
     if (!line.trim()) continue;
-    const [sha, short, subject, author, date, refs] = line.split("\x1f");
+    const [sha, short, subject, author, date, refs, parents] = line.split("\x1f");
     commits.push({
       sha,
       short,
@@ -638,6 +646,7 @@ async function listCommits(dir, { limit = 30, file = null } = {}) {
         .split(", ")
         .map((r) => r.trim())
         .filter(Boolean),
+      parents: (parents || "").split(" ").filter(Boolean),
     });
   }
   return commits;