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.

server/index.js

@@ -97,7 +97,6 @@ const remoteSourcesRouter = require("./routes/remote-sources");
 const metricsRouter = require("./routes/metrics");
 const lanesRouter = require("./routes/lanes");
 const locksRouter = require("./routes/locks");
-const skillsRouter = require("./routes/skills");
 
 const APP_VERSION = (() => {
   try {
@@ -141,7 +140,6 @@ function createApp() {
   app.use("/api/webhooks", webhooksRouter);
   app.use("/api/remote-sources", remoteSourcesRouter);
   app.use("/api/metrics", metricsRouter);
-  app.use("/api/skills", skillsRouter);
   app.get("/api/openapi.json", (_req, res) => {
     res.json(openApiSpec);
   });