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/LaneCard.tsx

@@ -271,7 +271,7 @@ export function since(sec: number | null): string {
 }
 
 /**
- * Repo tooling (agents install / MCP sync / dev-sync check, and the
+ * Repo tooling (MCP sync / dev-sync check, and the
  * create/update-readme run, which moved here from the Add-lane modal) for one lane,
  * collapsed into a single dropdown. Lives outside LaneCard so it can be
  * placed in the Workspace page header, next to "Add lane" — it polls its
@@ -281,16 +281,11 @@ export function since(sec: number | null): string {
 export function LaneToolsMenu({ lane }: { lane: Lane }) {
   const { t } = useTranslation(["lanes"]);
   const [toolsMenuOpen, setToolsMenuOpen] = useState(false);
-  const [laneActionBusy, setLaneActionBusy] = useState<
-    "agents" | "mcp" | "sync-check" | "docs" | null
-  >(null);
+  const [laneActionBusy, setLaneActionBusy] = useState<"mcp" | "sync-check" | "docs" | null>(null);
   const [laneActionResult, setLaneActionResult] = useState<string | null>(null);
   const runtime = useLaneRuntime(lane.id, 0);
 
-  const runLaneAction = async (
-    which: "agents" | "mcp" | "sync-check" | "docs",
-    fn: () => Promise<string>
-  ) => {
+  const runLaneAction = async (which: "mcp" | "sync-check" | "docs", fn: () => Promise<string>) => {
     setLaneActionBusy(which);
     setLaneActionResult(null);
     try {
@@ -302,12 +297,6 @@ export function LaneToolsMenu({ lane }: { lane: Lane }) {
     }
   };
 
-  const handleAgentsInstall = () =>
-    runLaneAction("agents", async () => {
-      const result = await api.lanes.agentsInstall(lane.id);
-      return t("actions.agentsInstallResult", { files: result.installed.join(", ") });
-    });
-
   // A skill only exists inside a CLI session, so there is nothing server-side
   // to call: this opens the lane's own terminal run with the slash command as
   // its first message. Claude-only — codex has no slash commands.
@@ -363,22 +352,6 @@ export function LaneToolsMenu({ lane }: { lane: Lane }) {
           role="menu"
           className="absolute right-0 z-10 mt-1 min-w-44 overflow-hidden rounded-md border border-border-light bg-surface-0 py-1 shadow-lg shadow-black/40"
         >
-          {/* Claude-only: other CLIs have no agents to install. */}
-          {lane.tool === "claude" && (
-            <button
-              type="button"
-              role="menuitem"
-              data-testid="lane-agents-install"
-              onClick={(e) => {
-                e.stopPropagation();
-                setToolsMenuOpen(false);
-                void handleAgentsInstall();
-              }}
-              className="block w-full px-3 py-1.5 text-left text-fg-secondary hover:bg-surface-2"
-            >
-              {t("actions.agentsInstall")}
-            </button>
-          )}
           {lane.tool === "claude" && (
             <button
               type="button"