refactor(lanes): drop the workflow skills and Superpowers link; pipelines go dormant

The plugin stops shipping its workflow layer:
- skills/ship-feature and skills/ship-feature-lane, the 18 stage/ship slash
  commands (plugin.json keeps agenthub-doctor/update/open), and all four
  agents/ (qc-local, senior-gate-reviewer, backend-reviewer, frontend-reviewer).
- CLI `agenthub skills install`, `agenthub lanes agents install`,
  `agenthub ship-full|ship-quick`; routes POST /api/skills/install and
  POST /api/lanes/:id/agents/install; the Settings button, the lane Tools
  menu item and the Add-lane setup step that called them.
- The Superpowers auto-install: server/lib/skill-plugins.js, the bootstrap's
  autoInstallSkillPlugins / skillPluginsSettled gate and the doctor row.

Pipelines are kept but dormant: server/data/pipelines/ is deleted, so no
template ships. `default` resolves to EMPTY_PIPELINE (no nodes, progress 0),
createLane still accepts it, POST /api/lanes/:id/stage answers 400
ENOPIPELINE, and the Workspace hides the stage timer, pickers, PipelineMap
and strip stage chip for a lane with no nodes. A template dropped into
DASHBOARD_PIPELINES_DIR turns it all back on. The server suite loads its
templates from server/__tests__/fixtures/pipelines/.

Docs: CLAUDE.md (marker, retired rules), README(.vi), INSTALL, ARCHITECTURE,
docs/LANES|PLUGINS|CLI|API, agenthub-introduction.html.

client/src/components/lanes/__tests__/LaneCard.test.tsx

@@ -23,7 +23,6 @@ vi.mock("../../../lib/api", () => ({
       up: vi.fn(),
       down: vi.fn(),
       preflight: vi.fn().mockResolvedValue({ blocked: [], warnings: [] }),
-      agentsInstall: vi.fn(),
       mcpSync: vi.fn(),
       syncBaseCheck: vi.fn(),
       routerApply: vi.fn(),
@@ -309,17 +308,6 @@ describe("LaneToolsMenu", () => {
     } as unknown as LaneRuntime);
   });
 
-  it("clicking Install agents calls the API and shows the result", async () => {
-    vi.mocked(api.lanes.agentsInstall).mockResolvedValue({
-      installed: ["qc-local.md", "senior-gate-reviewer.md"],
-    });
-    render(<LaneToolsMenu lane={makeLane()} />);
-    await userEvent.click(await screen.findByTestId("lane-tools-menu"));
-    await userEvent.click(await screen.findByTestId("lane-agents-install"));
-    await waitFor(() => expect(api.lanes.agentsInstall).toHaveBeenCalledWith(1));
-    expect(await screen.findByTestId("lane-action-result")).toHaveTextContent("qc-local.md");
-  });
-
   it("clicking Sync MCP calls the API and shows the result", async () => {
     vi.mocked(api.lanes.mcpSync).mockResolvedValue({
       servers: ["playwright"],