feat: Directory agent status + plugin modal rework, Vault restyle, navbar (v1.24.0)

- Merge theta-agent into Directory: remove the Agents page; add green/yellow/red
  status dots to host rows and a Metrics tab (telemetry + discovery) to the
  resource modal, joined to hosts by hostname, live via socket.io + 30s refresh.
- Discovery Plugins New-plugin modal: slug derived from name (field removed),
  cron dropdown (hourly/daily/weekly/custom), configSchema-driven settings
  (Proxmox url/tokenId/tokenSecret) sent as a populated config.
- Directory resource slug now read-only + derived from name.
- Vault page restyled to match the site.
- Navbar: username no longer underlined; only the active link is bold+underlined.
- docs/agents.md: document the Directory status/metrics + NAT troubleshooting.

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

nodejs/routes/index.js

@@ -59,12 +59,6 @@ router.get('/overview', function(req, res) {
   res.render('overview', {...values});
 });
 
-// Connected theta-agent hosts + live telemetry (admin). Data from
-// GET /api/agent/nodes; live updates via socket.io 'agent.*' events.
-router.get('/agents', function(req, res) {
-  res.render('agents', {...values});
-});
-
 router.get('/admin', (req, res) => res.redirect(301, '/overview'));
 router.get('/notifications', (req, res) => res.redirect(301, '/overview'));
 router.get('/dashboard', (req, res) => res.redirect(301, '/overview'));