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/pages/__tests__/SessionDetail.nestedAgents.test.tsx

@@ -48,6 +48,11 @@ const mockSession: Session = {
 let mockAgents: Agent[] = [];
 let mockCost: { total_cost: number; breakdown: unknown[] } = { total_cost: 0, breakdown: [] };
 
+// The header's Resume reads lanes and runs; this file is about the agent tree.
+vi.mock("../../components/lanes/SessionResumeButton", () => ({
+  SessionResumeButton: () => null,
+}));
+
 vi.mock("../../lib/api", () => ({
   api: {
     sessions: {