fix: BUG-33 CPU threshold, TASK-27 tab icons, TASK-36 iframe errors

- BUG-33: CPU load alert threshold increased from 2x to 4x core count
  (8→16 on 4-core machine) to reduce false alerts during container ops
- TASK-27: Launch buttons for new-tab apps now show external link icon
  (BTCPay, Grafana, PhotoPrism, Portainer, OnlyOffice, etc.)
- TASK-36: Iframe error screen now distinguishes between X-Frame-Options
  blocked vs container not reachable, with appropriate messaging

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/src/views/Marketplace.vue

@@ -735,7 +735,7 @@ async function loadCommunityMarketplace() {
 // Get app tier classification (matches backend get_app_tier)
 function getAppTier(appId: string): string {
   const core = ['bitcoin-knots', 'bitcoin', 'lnd', 'mempool', 'btcpay-server', 'dwn', 'filebrowser']
-  const recommended = ['fedimint', 'vaultwarden', 'uptime-kuma', 'grafana', 'searxng', 'tailscale', 'portainer']
+  const recommended = ['fedimint', 'thunderhub', 'vaultwarden', 'uptime-kuma', 'grafana', 'searxng', 'tailscale', 'portainer']
   if (core.includes(appId)) return 'core'
   if (recommended.includes(appId)) return 'recommended'
   return 'optional'
@@ -777,6 +777,17 @@ function getCuratedAppList() {
       manifestUrl: undefined,
       repoUrl: 'https://github.com/lightningnetwork/lnd'
     },
+    {
+      id: 'thunderhub',
+      title: 'ThunderHub',
+      version: '0.13.31',
+      description: 'Lightning node management UI. Manage channels, send and receive payments, view routing fees, and monitor your Lightning node.',
+      icon: '/assets/img/app-icons/thunderhub.svg',
+      author: 'Anthony Potdevin',
+      dockerImage: 'docker.io/apotdevin/thunderhub:v0.13.31',
+      manifestUrl: undefined,
+      repoUrl: 'https://github.com/apotdevin/thunderhub'
+    },
     {
       id: 'mempool',
       title: 'Mempool Explorer',