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/__tests__/git-diff-ops.test.js

@@ -19,6 +19,7 @@ const {
   listCommits,
   listPaths,
   listTree,
+  listTreeAll,
   parseUnifiedDiff,
   readFileAt,
 } = require("../lib/git-diff");
@@ -456,6 +457,22 @@ describe("listCommits / readFileAt / listPaths / listTree", () => {
     );
     await assert.rejects(() => listTree(LANE, { subdir: "../.." }), { code: "EBADPATH" });
   });
+
+  it("reads every level of the tree in one pass, grouped like listTree", async () => {
+    write(LANE, "src/api/x.ts", "x\n");
+    write(LANE, "src/main.ts", "m\n");
+    gc(LANE, "add", "-A");
+    gc(LANE, "commit", "-qm", "src");
+
+    const all = await listTreeAll(LANE);
+    assert.equal(all.truncated, false);
+    // Each level equals what the one-level read returns for it.
+    for (const level of ["", "src", "src/api"]) {
+      const one = await listTree(LANE, { subdir: level });
+      assert.deepEqual(all.levels[level], one.entries, level);
+    }
+    assert.deepEqual(Object.keys(all.levels).sort(), ["", "src", "src/api"]);
+  });
 });
 
 describe("runGitAction — per-file staging, discard and branches", () => {