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.

client/src/lib/api.ts

@@ -2462,6 +2462,16 @@ export const api = {
      * @param id The lane id.
      * @param path Repo-relative directory; "" for the repo root.
      */
+    /**
+     * GET /api/lanes/:id/git/tree-all — every level of the tracked tree in one
+     * read, keyed by directory ("" is the root), each shaped like `gitTree`'s.
+     */
+    gitTreeAll: (id: number) =>
+      request<{
+        available: boolean;
+        levels: Record<string, LaneTreeEntry[]>;
+        truncated: boolean;
+      }>(`/lanes/${id}/git/tree-all`),
     gitTree: (id: number, path = "") =>
       request<{
         available: boolean;