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/public/css/styles.css

@@ -3,6 +3,12 @@ nav.navbar{
 	padding-right: 1em;
 }
 
+/* Only the active top-nav link is bold + underlined; the username is plain. */
+.top-nav a.active{
+	font-weight: bold;
+	text-decoration: underline;
+}
+
 body {
 	display: flex;
 	flex-direction: column;