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/pages/Workspace.tsx

@@ -53,6 +53,7 @@ import {
   PanelLeftClose,
   ChevronsLeftRight,
   PanelRightClose,
+  Maximize2,
 } from "lucide-react";
 import { api } from "../lib/api";
 import type { CwdSuggestion, RunListResponse } from "../lib/api";
@@ -88,21 +89,25 @@ const CHANGES_SIZE_KEY = "agenthub.workspace.changesSize";
 /** The three widths the Changes panel cycles through, then closed. Reading a
  *  diff and watching a console want opposite amounts of room, and which one is
  *  "work" changes several times an hour — hence ONE control that steps
- *  narrow → 50/50 → 70/30 → closed, rather than a width button beside a
+ *  narrow → 50/50 → 70/30 → full → closed, rather than a width button beside a
  *  collapse button that both live in the panel's tightest corner. */
-const CHANGES_SIZES = ["compact", "half", "wide"] as const;
+const CHANGES_SIZES = ["compact", "half", "wide", "full"] as const;
 type ChangesSize = (typeof CHANGES_SIZES)[number];
 const CHANGES_WIDTH: Record<ChangesSize, string> = {
   compact: "w-[28rem] xl:w-[34rem]",
   half: "w-1/2",
   wide: "w-[70%]",
+  // The console beside it is HIDDEN, not unmounted: a live run's terminal
+  // and a half-typed prompt must survive a round trip through full width.
+  full: "w-full",
 };
 /** The icon the one resize control shows AT each size: what the next click
  *  gives you — an even split, a wider panel, then closed. */
 const CHANGES_NEXT_ICON: Record<ChangesSize, typeof Columns2> = {
   compact: Columns2,
   half: ChevronsLeftRight,
-  wide: PanelRightClose,
+  wide: Maximize2,
+  full: PanelRightClose,
 };
 
 // ── Page ──────────────────────────────────────────────────────────────
@@ -733,7 +738,9 @@ export function Workspace() {
         <div className="flex min-h-0 flex-1 gap-4">
           <section
             data-testid="lane-detail"
-            className={`flex min-h-0 min-w-0 flex-1 flex-col ${currentLane ? "card p-4" : ""}`}
+            className={`flex min-h-0 min-w-0 flex-1 flex-col ${currentLane ? "card p-4" : ""}${
+              currentLane && changesOpen && changesSize === "full" ? " hidden" : ""
+            }`}
           >
             {/* One header row, not two. The pipeline picker, the stage badges,
               the feature picker and the router select used to sit on a second