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/AddLaneModal.tsx

@@ -115,7 +115,6 @@ export function AddLaneModal({
   const [browseOpen, setBrowseOpen] = useState(false);
   const [setupResult, setSetupResult] = useState<{
     profile: "scaffolded" | "skipped" | "failed";
-    agents: "ok" | "failed";
     mcp: "ok" | "failed";
     router: "ok" | "skipped" | "failed";
   } | null>(null);
@@ -294,7 +293,7 @@ export function AddLaneModal({
       // POST /worktree returns as soon as the DB row exists (202) — the
       // actual `git worktree add` runs afterward, in the background, on the
       // server. Firing setup against the lane's cwd before that finishes
-      // means agents/mcp write into a directory that doesn't exist yet, so
+      // means mcp writes into a directory that doesn't exist yet, so
       // wait for provisioning to leave the "provisioning" status first.
       const provisionedLane = await waitForProvisioned(result.lane.id);
       if (!provisionedLane || provisionedLane.status === "failed") {
@@ -303,9 +302,8 @@ export function AddLaneModal({
         return;
       }
 
-      const [profileOutcome, agentsOutcome, mcpOutcome, routerOutcome] = await Promise.allSettled([
+      const [profileOutcome, mcpOutcome, routerOutcome] = await Promise.allSettled([
         api.lanes.profileInit(result.lane.id),
-        api.lanes.agentsInstall(result.lane.id),
         api.lanes.mcpSync(result.lane.id),
         applyRouter(result.lane.id),
       ]);
@@ -316,7 +314,6 @@ export function AddLaneModal({
               ? "scaffolded"
               : "skipped"
             : "failed",
-        agents: agentsOutcome.status === "fulfilled" ? "ok" : "failed",
         mcp: mcpOutcome.status === "fulfilled" ? "ok" : "failed",
         router:
           routerOutcome.status !== "fulfilled" ? "failed" : router === "native" ? "skipped" : "ok",
@@ -328,7 +325,6 @@ export function AddLaneModal({
         console.info("[add-lane] auto-setup result:", {
           profile:
             profileOutcome.status === "fulfilled" ? profileOutcome.value : profileOutcome.reason,
-          agents: agentsOutcome.status === "fulfilled" ? agentsOutcome.value : agentsOutcome.reason,
           mcp: mcpOutcome.status === "fulfilled" ? mcpOutcome.value : mcpOutcome.reason,
           // Never the profile itself: it would put an endpoint and a lane id in
           // the browser console. (The key is never sent here at all.)
@@ -740,7 +736,6 @@ export function AddLaneModal({
                   ok: setupResult.profile !== "failed",
                   skipped: setupResult.profile === "skipped",
                 },
-                { label: t("addLaneSetupAgents"), ok: setupResult.agents === "ok" },
                 { label: t("addLaneSetupMcp"), ok: setupResult.mcp === "ok" },
                 {
                   label: t("addLaneSetupRouter"),