feat(workspace): the console tab bar is the session view's only header

The status/name/back-arrow row is gone; Tools sits at the tab bar's right
end and the pipeline/feature pickers show only with a template.
LaneConsolePane is reduced to the terminal (no title, no Active runs, no
New run): RunHistory.tsx, api.run.history and the page's active-sessions
poll are removed.

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

@@ -173,13 +173,6 @@ vi.mock("../../lib/api", async (importOriginal) => {
           recordCall("GET", "/api/run/list");
           return { runs: [], items: [] };
         }),
-        history: vi.fn().mockImplementation(async (limit?: number, opts?: { laneId?: number }) => {
-          recordCall(
-            "GET",
-            `/api/run/history?limit=${limit}${opts?.laneId ? `&laneId=${opts.laneId}` : ""}`
-          );
-          return { items: [] };
-        }),
         binary: vi.fn().mockImplementation(async () => {
           recordCall("GET", "/api/run/binary");
           return { found: true, path: "/usr/bin/claude" };
@@ -612,7 +605,7 @@ describe("Workspace — home and session view", () => {
     expect(screen.getByTestId("lane-detail").parentElement).toHaveClass("hidden");
   });
 
-  it("opens the session view for ?run=, and the back button returns home", async () => {
+  it("opens the session view for ?run=, headed by the tab bar alone", async () => {
     render(
       <MemoryRouter initialEntries={["/workspace?lane=1&run=agenthub-lane-1"]}>
         <Workspace />
@@ -622,8 +615,10 @@ describe("Workspace — home and session view", () => {
     await settle();
     expect(screen.queryByTestId("workspace-home")).toBeNull();
     expect(screen.getByTestId("lane-detail").parentElement).not.toHaveClass("hidden");
-    await userEvent.setup().click(screen.getByTestId("workspace-back-home"));
-    expect(await screen.findByTestId("workspace-home")).toBeInTheDocument();
+    // No header row (status, back arrow, name) and no pane header: the tab bar is it.
+    expect(screen.queryByTestId("workspace-back-home")).toBeNull();
+    expect(screen.queryByText(/^Run /)).toBeNull();
+    expect(screen.getByTestId("console-tab-new")).toBeInTheDocument();
   });
 
   it("opens an ended session's replay for ?session=, hiding (not unmounting) the console", async () => {