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.

scripts/plugin-doctor.js

@@ -6,10 +6,8 @@
  * declared package, not just that node_modules exists), server liveness,
  * duplicate hook entries (the one failure that silently doubles every token and
  * cost figure), the `agenthub` CLI launcher and its PATH, the `tmux` binary
- * every browser-started run depends on, whether the slash
- * commands the pipeline templates name as node drivers are actually resolvable
- * (the `superpowers` plugin, today), and the dashboard bundle — quoting the last
- * build error when it is missing.
+ * every browser-started run depends on, and the dashboard bundle — quoting the
+ * last build error when it is missing.
  * Read-only — it diagnoses, it never repairs.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
@@ -85,7 +83,6 @@ function diagnose() {
   add(...cliStatus());
   add(...systemdStatus());
   add(...tmuxStatus());
-  add(...skillPluginStatus());
 
   add(...dashboardUiStatus(rt));
 
@@ -190,37 +187,6 @@ function lastBuildError(logPath) {
   return hit ? hit.trim().slice(0, 200) : null;
 }
 
-/**
- * WARN (never FAIL) when a plugin the pipelines depend on cannot be resolved:
- * the dashboard, hooks and CLI all work without it — only the pipeline
- * skills that drive it stop partway, so this must not fail a doctor run.
- *
- * The requirement derivation and the missing/satisfied rules live in
- * `server/lib/skill-plugins.js`, shared with the bootstrap that installs them.
- */
-function skillPluginStatus() {
-  const skillPlugins = require("../server/lib/skill-plugins");
-  const required = skillPlugins.requiredSkillPlugins();
-  if (!required.size) return ["ok", "Skill plugins", "no pipeline names an external plugin"];
-
-  let missing;
-  try {
-    missing = skillPlugins.missingSkillPlugins();
-  } catch {
-    return ["warn", "Skill plugins", "could not read the installed-plugin manifest"];
-  }
-  if (!missing.length) {
-    return ["ok", "Skill plugins", `${[...required.keys()].sort().join(", ")} available`];
-  }
-  return [
-    "warn",
-    "Skill plugins",
-    `${missing.map((m) => `${m.name} (needed for ${m.skills.join(", ")})`).join("; ")} — ` +
-      `the pipelines name these commands; install with ` +
-      `claude plugin install ${missing.map((m) => m.autoInstall?.spec || m.name).join(" ")}`,
-  ];
-}
-
 /**
  * The failure this row exists for is silent by construction: a unit still
  * naming a retired plugin cache directory keeps a running dashboard looking
@@ -275,8 +241,8 @@ function systemdStatus() {
  * WARN (never FAIL) when `tmux` is absent: every run the dashboard starts is a
  * tmux session (`server/lib/tmux.js`), so without the binary the run console,
  * `agenthub lanes shell` and the session-reload keystrokes all fail — while
- * sessions, analytics, lanes and the CLI keep working. Same reasoning as the
- * skill-plugins row: a partial feature loss must not fail a doctor run.
+ * sessions, analytics, lanes and the CLI keep working. A partial feature
+ * loss must not fail a doctor run.
  *
  * This checks the doctor's own PATH. A server started as a systemd `--user`
  * service can still see a different one — `GET /api/run/tmux` is the server's