feat(infra): commit live infra-audit/cluster work to reconcile git with prod

This work (network_hosts inventory + infra_audit MCP tool, /api/cluster +
Sacred Valley cluster card, topbar cluster-health pill + SW self-heal) was
built in an earlier session and DEPLOYED to CT 311 as alpha.24–26, but was
never committed to git — prod was running code absent from the repo. Commits
it as-is (already prod-validated) so git matches the live state, and restores
its alpha.24/25/26 CHANGELOG entries. Files are disjoint from the fold-in
work; both now ship together under alpha.27.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/api/routes/cluster.js

@@ -0,0 +1,17 @@
+import { Router } from 'express';
+import { asyncWrap } from '../errors.js';
+import { clusterHealth } from '../../proxmox/cluster.js';
+
+// Read-only cluster health for the Sacred Valley card. Cached briefly so multiple
+// polling clients coalesce into one PVE call. Owner or any authed agent.
+export const router = Router();
+
+let cache = { at: 0, data: null };
+const TTL = 10_000;
+
+router.get('/', asyncWrap(async (_req, res) => {
+  if (cache.data && Date.now() - cache.at < TTL) return res.json(cache.data);
+  const data = await clusterHealth();
+  cache = { at: Date.now(), data };
+  res.json(data);
+}));