feat(workspace): the home's context card follows the scroll; no scrollbar

On the workspace home the Instructions / Memory / Context / Folder card is
sticky inside the home's scroller (scrolling itself, barless, when taller
than the window), and the home column hides its scrollbar — wheel and touch
still scroll it.

client/src/components/lanes/WorkspaceContext.tsx

@@ -2,7 +2,8 @@
  * @file WorkspaceContext — a workspace's context: Instructions, Memory
  * (read-only), Context files and Folders (`GET/PUT/POST/DELETE
  * /api/lanes/:id/sources…`, see server/lib/lane-sources.js). Shown as the
- * workspace home's right column and, `compact`, folded at the bottom of the
+ * workspace home's right column (sticky: it follows the home's scroll) and,
+ * `compact`, folded at the bottom of the
  * session view's Changes panel. Folder suggestions are the repo's untracked
  * worktrees from `GET /api/projects`, filtered by Settings → Worktrees; the
  * same form clones related repos beside the workspace (`CloneSourcesForm`).
@@ -157,7 +158,13 @@ function ContextBody({
       <aside
         data-testid="workspace-context"
         aria-label={t("home.contextPanel")}
-        className={compact ? "" : "card w-80 shrink-0 self-start p-0"}
+        // On the home it follows the scroll (sticky in the home's scroller),
+        // scrolling itself — without a bar — when taller than the window.
+        className={
+          compact
+            ? ""
+            : "card no-scrollbar sticky top-2 max-h-[calc(100vh-7rem)] w-80 shrink-0 self-start overflow-y-auto p-0"
+        }
       >
         {view && !view.supported && (
           <p className="border-b border-border px-4 py-3 text-xs text-status-warning">

client/src/pages/Workspace.tsx

@@ -1358,7 +1358,8 @@ export function Workspace() {
               // `relative`: the home's absolutely placed bits (a row's sr-only
               // label) must be clipped by THIS scroller — placed against the
               // row outside it they stretched the page into an empty scroll.
-              className={`relative min-h-0 min-w-0 flex-1 overflow-y-auto${
+              // No visible scrollbar: the wheel and touch still scroll it.
+              className={`no-scrollbar relative min-h-0 min-w-0 flex-1 overflow-y-auto${
                 changesOpen && changesFull ? " hidden" : ""
               }${changesOpen && !changesFull ? " pr-5" : ""}`}
             >

client/src/pages/__tests__/Workspace.test.tsx

@@ -1208,7 +1208,11 @@ describe("Workspace — home and session view", () => {
     expect(screen.getByTestId("workspace-home-column").parentElement).not.toHaveClass("hidden");
     // Its own scroller contains its absolutely placed bits (sr-only labels),
     // or they stretch the page past the viewport.
-    expect(screen.getByTestId("workspace-home-column")).toHaveClass("relative", "overflow-y-auto");
+    expect(screen.getByTestId("workspace-home-column")).toHaveClass(
+      "relative",
+      "overflow-y-auto",
+      "no-scrollbar"
+    );
     expect(
       screen.queryByTestId("lane-changes-card") ?? screen.queryByTestId("lane-changes-expand")
     ).not.toBeNull();