feat(lanes): full-width Changes, Stage all, one-read expand-all

- The Changes panel's width control gains a full-width step (narrow →
  50/50 → 70/30 → full → closed); the console beside it is hidden with
  CSS, never unmounted.
- "Expand all folders" is one GET /api/lanes/:id/git/tree-all (one
  `git ls-files`, every level shaped like /git/tree) instead of one
  request and one git process per folder.
- Overview: a Stage all button and the staged-only commit box sit above
  the file list and stay pinned while it scrolls; the Files finder is
  pinned too.

server/lib/git-diff.js

@@ -785,12 +785,50 @@ async function listTree(dir, { subdir = "" } = {}) {
   };
 }
 
+/**
+ * Every level of the tracked tree from ONE `git ls-files`, keyed by directory
+ * path ("" is the root), each level shaped and capped exactly like
+ * `listTree`'s. "Expand all folders" used to be one request — one ls-files —
+ * per folder, which on a large repo is thousands of git processes.
+ */
+async function listTreeAll(dir) {
+  const { all, cut } = await lsFiles(dir, []);
+  const byDir = new Map();
+  const level = (d) => {
+    let l = byDir.get(d);
+    if (!l) byDir.set(d, (l = { dirs: new Set(), files: [] }));
+    return l;
+  };
+  level("");
+  for (const p of all) {
+    const parts = p.split("/");
+    for (let i = 0; i < parts.length - 1; i++) {
+      level(parts.slice(0, i).join("/")).dirs.add(parts[i]);
+    }
+    const parent = parts.slice(0, -1).join("/");
+    level(parent).files.push({ name: parts[parts.length - 1], path: p, dir: false });
+  }
+  const levels = {};
+  let truncated = cut;
+  for (const [d, { dirs, files }] of byDir) {
+    const prefix = d ? `${d}/` : "";
+    const entries = [
+      ...[...dirs].sort().map((name) => ({ name, path: `${prefix}${name}`, dir: true })),
+      ...files.sort((a, b) => a.name.localeCompare(b.name)),
+    ];
+    if (entries.length > MAX_PATHS) truncated = true;
+    levels[d] = entries.slice(0, MAX_PATHS);
+  }
+  return { levels, truncated };
+}
+
 module.exports = {
   collectChanges,
   laneStatus,
   listCommits,
   listPaths,
   listTree,
+  listTreeAll,
   parseNumstat,
   parsePorcelainZ,
   parseUnifiedDiff,