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/utils/ui.js

@@ -46,7 +46,6 @@ module.exports = {
 		{href: '/directory', icon: 'fa-solid fa-server', label: 'Directory', groups: ['app_sso_admin', 'app_sso_directory_admin', 'admin']},
 		// Vault requires login - per-user secrets at secret/users/<uid>/*.
 		{href: '/vault', icon: 'fa-solid fa-vault', label: 'Vault', groups: ['login']},
-		{href: '/agents', icon: 'fa-solid fa-microchip', label: 'Agents', groups: ['app_sso_admin', 'admin']},
 		{href: '/overview', icon: 'fa-solid fa-gauge-high', label: 'Overview', groups: ['app_sso_admin', 'admin']},
 	],
 };