feat(ui): finish the workspace-sessions plan — tool filter, session search, explicit Resume

- Sidebar: a tool filter (shown once workspaces of two tools exist, kept in
  agenthub.sidebar.projects → tool; reordering under it keeps the hidden
  workspaces' places), and search that also finds a workspace by one of its
  session names, showing only the matching sessions.
- Workspace home: the repository it belongs to (root, main branch, worktree
  count) under the title, and each recent's cost.
- Transcript page: an explicit Resume for a Claude session started in a
  workspace's own folder (SessionResumeButton). It warns that a resume re-reads
  the whole transcript, re-reads the live panes, then starts in the first free
  pane and opens it; a live session offers Open pane instead.

client/src/components/__tests__/WorkspaceTree.test.tsx

@@ -190,6 +190,64 @@ describe("WorkspaceTree", () => {
     expect(rowIds()).toEqual(["workspace-row-3"]);
   });
 
+  it("filters by tool, remembered, and offers the filter only with two tools", async () => {
+    const user = userEvent.setup();
+    const { unmount } = renderTree();
+    await screen.findByTestId("workspace-row-1");
+    await user.selectOptions(screen.getByLabelText("Filter by tool"), "codex");
+    expect(rowIds()).toEqual(["workspace-row-3"]);
+    expect(JSON.parse(localStorage.getItem("agenthub.sidebar.projects")!).tool).toBe("codex");
+    await user.selectOptions(screen.getByLabelText("Filter by tool"), "");
+    expect(rowIds()).toEqual(["workspace-row-1", "workspace-row-2", "workspace-row-3"]);
+    unmount();
+
+    // One tool only: no filter, and a stale stored one is ignored.
+    localStorage.setItem("agenthub.sidebar.projects", JSON.stringify({ tool: "codex" }));
+    lanes = lanes.filter((l) => l.tool === "claude");
+    renderTree();
+    await screen.findByTestId("workspace-row-1");
+    expect(screen.queryByLabelText("Filter by tool")).toBeNull();
+    expect(rowIds()).toEqual(["workspace-row-1", "workspace-row-2"]);
+  });
+
+  it("reorders within a tool filter without losing the hidden workspaces' places", async () => {
+    localStorage.setItem("agenthub.workspace.laneOrder", JSON.stringify([1, 3, 2]));
+    localStorage.setItem("agenthub.sidebar.projects", JSON.stringify({ tool: "claude" }));
+    renderTree();
+    fireEvent.keyDown(await screen.findByTestId("workspace-open-2"), {
+      key: "ArrowUp",
+      altKey: true,
+    });
+    expect(JSON.parse(localStorage.getItem("agenthub.workspace.laneOrder")!)).toEqual([2, 3, 1]);
+    expect(rowIds()).toEqual(["workspace-row-2", "workspace-row-1"]);
+  });
+
+  it("finds a workspace by one of its session names, showing only the matches", async () => {
+    vi.mocked(api.sessions.list).mockImplementation(async (params) => ({
+      sessions:
+        (params as { cwd?: string }).cwd === "/r/sub"
+          ? [session("s-x", "Fix login bug"), session("s-y", "Docs")]
+          : [session("s-live", "Live one"), session("s-old", "Old one")],
+      total: 2,
+      limit: 20,
+      offset: 0,
+    }));
+    const user = userEvent.setup();
+    renderTree();
+    await screen.findByTestId("workspace-row-1");
+    await user.click(screen.getByRole("button", { name: "Search workspaces and sessions" }));
+    await user.type(screen.getByRole("searchbox"), "login");
+    await waitFor(() => expect(rowIds()).toEqual(["workspace-row-2"]));
+    expect(screen.getByTestId("workspace-session-s-x")).toBeVisible();
+    expect(screen.queryByTestId("workspace-session-s-y")).toBeNull();
+
+    // A workspace whose NAME matches keeps all of its sessions.
+    await user.clear(screen.getByRole("searchbox"));
+    await user.type(screen.getByRole("searchbox"), "sub");
+    await waitFor(() => expect(rowIds()).toEqual(["workspace-row-2"]));
+    expect(screen.getByTestId("workspace-session-s-y")).toBeInTheDocument();
+  });
+
   it("offers Reset only on a managed workspace and the readme run only on claude", async () => {
     const user = userEvent.setup();
     renderTree();