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-bootstrap.js

@@ -161,10 +161,6 @@ function fastPathOk(rt = runtimeDir()) {
   if (state.pluginRoot !== PLUGIN_ROOT) return false;
   if (state.depsHash !== depsHash()) return false;
   if (!fs.existsSync(path.join(rt, "node_modules"))) return false;
-  // A machine can be fully set up and still be missing the plugins the
-  // pipelines drive. Reading one recorded flag keeps this hot path cheap — the
-  // actual check (manifest + every user SKILL.md) runs once, in the worker.
-  if (!state.skillPluginsSettled) return false;
   // A live server says nothing about whether it will come back. When our unit
   // still names a previous plugin cache directory, everything looks healthy
   // until the next reboot — and then the dashboard is simply gone, from a path
@@ -500,46 +496,6 @@ function log(rt, line) {
   }
 }
 
-/**
- * Install the plugins AgentHub's pipelines drive but this machine cannot resolve —
- * today `superpowers`, which `/agenthub:ship-feature(-lane)` calls step by step. A
- * fresh `agenthub` install otherwise runs those skills partway and fails at the
- * first call with no warning beforehand.
- *
- * Off by setting `AGENTHUB_AUTO_INSTALL_PLUGINS` to `0`, `false` or `off`; that
- * leaves `/agenthub-doctor`'s WARN row as the only notice, which is the right
- * behaviour for anyone who wants to choose their own plugins.
- *
- * One-shot: the outcome is recorded in the runtime state and the fast path
- * takes it into account, so a machine with no network does not re-attempt a
- * clone on every session. `/agenthub-update` (`--force`) retries.
- *
- * Best-effort throughout. Nothing here may throw or block: the dashboard,
- * hooks and CLI all work without these plugins.
- *
- * @returns {"off"|"nothing-missing"|"installed"|"failed"|"error"} or the previously
- *   recorded outcome when this run had nothing to settle.
- */
-function autoInstallSkillPlugins(rt, { force = false } = {}) {
-  const flag = process.env.AGENTHUB_AUTO_INSTALL_PLUGINS;
-  if (flag === "0" || flag === "false" || flag === "off") return "off";
-  // Return the PREVIOUS outcome, not a marker: writeState records whatever this
-  // returns, and overwriting "installed" with "already-settled" would lose the
-  // only record of what actually happened.
-  const settled = readState(rt)?.skillPluginsSettled;
-  if (!force && settled) return settled;
-
-  try {
-    const { autoInstallSkillPlugins: install } = require("../server/lib/skill-plugins");
-    const summary = install((line) => log(rt, line));
-    if (!summary.attempted.length) return "nothing-missing";
-    return summary.failed.length ? "failed" : "installed";
-  } catch (err) {
-    log(rt, `skill-plugin auto-install skipped: ${err.message}`);
-    return "error";
-  }
-}
-
 /* ------------------------------------------------------ plugin-cache pruning */
 
 /** How many retired builds to leave behind, newest first, as a rollback cushion. */
@@ -814,21 +770,12 @@ function bootstrap(rt = runtimeDir(), { force = false } = {}) {
       }
     }
 
-    // Last, and deliberately so: it clones from the network, and nothing above
-    // may wait on it. Runs here rather than in the foreground pass because this
-    // whole function is already detached from the 10 s SessionStart hook.
-    const skillPlugins = autoInstallSkillPlugins(rt, { force });
-
     writeState(
       {
         pluginVersion: pluginVersion(),
         depsHash: wantDeps,
         pluginRoot: PLUGIN_ROOT,
         claudeHome: getClaudeHome(),
-        // Settles the fast path: whatever the outcome, the next SessionStart
-        // must not spawn a worker just to retry a network clone. Cleared by
-        // `/agenthub-update` (force), which is the retry.
-        skillPluginsSettled: skillPlugins,
         updatedAt: new Date().toISOString(),
       },
       rt
@@ -930,6 +877,5 @@ module.exports = {
   livePids,
   stopDashboard,
   startDashboard,
-  autoInstallSkillPlugins,
   bootstrap,
 };