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/pages/__tests__/__snapshots__/screens.snapshot.test.tsx.snap

@@ -8435,44 +8435,11 @@ exports[`screen snapshots > Settings 1`] = `
       <p
         class="text-xs text-fg-muted mb-4"
       >
-        Machine-wide housekeeping and one-time setup for the ship-feature-lane pipeline.
+        Machine-wide lane housekeeping.
       </p>
       <div
         class="card p-5 space-y-4"
       >
-        <div
-          class="flex items-center justify-between flex-wrap gap-3"
-        >
-          <span
-            class="text-xs text-fg-secondary"
-          >
-            Install ship-feature-lane skill
-          </span>
-          <button
-            class="btn-ghost text-xs disabled:opacity-50"
-          >
-            <svg
-              class="lucide lucide-rotate-ccw w-3.5 h-3.5"
-              fill="none"
-              height="24"
-              stroke="currentColor"
-              stroke-linecap="round"
-              stroke-linejoin="round"
-              stroke-width="2"
-              viewBox="0 0 24 24"
-              width="24"
-              xmlns="http://www.w3.org/2000/svg"
-            >
-              <path
-                d="M3 12a9 9 0 1 0 9-9 9.75 9.75 0 0 0-6.74 2.74L3 8"
-              />
-              <path
-                d="M3 3v5h5"
-              />
-            </svg>
-            Install ship-feature-lane skill
-          </button>
-        </div>
         <div
           class="flex items-center justify-between flex-wrap gap-3"
         >