feat(demo): app launch UIs, "No demo" gating, onboarding skip, 12 nodes

App launching (DEMO):
- resolveAppUrl routes every app to its demo target: mock UIs for Bitcoin Core,
  ElectrumX, Fedimint (served by the backend), IndeeHub → iframe indee.tx1138.com,
  Mempool → mempool.space/testnet (new tab); all others → a generic "Demo preview"
  notice page.
- Non-demoable apps show a disabled "No demo" install button (marketplace details,
  app grid, featured apps).

Onboarding:
- Demo treats the visitor as fully set up so the onboarding WIZARD (seed/identity)
  is never forced; the welcome intro still replays per day. Intro CTA goes straight
  to login; wizard entry points + login restart-onboarding link hidden in demo.

Network:
- federation.list-nodes now returns 12 trusted/federated nodes (9 trusted, 3
  observer); transport.peers already at 5.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

neode-ui/src/composables/useDemoIntro.ts

@@ -47,3 +47,43 @@ export function clearDemoIntroSeen(): void {
     /* ignore */
   }
 }
+
+// ── Demoable apps ───────────────────────────────────────────────────────────
+// Only these apps actually do something in the demo (a mock UI or a real
+// external site). Everything else shows "No demo" on a disabled install button
+// and is not launchable.
+const DEMO_EXTERNAL_URLS: Record<string, string> = {
+  // Real, public sites that we open instead of mocking.
+  indeedhub: 'https://indee.tx1138.com/',
+  mempool: 'https://mempool.space/testnet',
+  'mempool-web': 'https://mempool.space/testnet',
+}
+
+// Apps with a same-origin mock UI served by the demo backend.
+const DEMO_MOCK_UI: Record<string, string> = {
+  'bitcoin-knots': '/app/bitcoin-ui/',
+  'bitcoin-core': '/app/bitcoin-ui/',
+  bitcoin: '/app/bitcoin-ui/',
+  'bitcoin-ui': '/app/bitcoin-ui/',
+  electrs: '/app/electrumx/',
+  electrumx: '/app/electrumx/',
+  'archy-electrs-ui': '/app/electrumx/',
+  fedimint: '/app/fedimint/',
+  fedimintd: '/app/fedimint/',
+  filebrowser: '/app/filebrowser/',
+}
+
+/** Apps that open in a new tab (external real sites) rather than an iframe. */
+export function isDemoExternal(appId: string): boolean {
+  return appId === 'mempool' || appId === 'mempool-web'
+}
+
+/** Can this app be launched/installed in the demo? */
+export function isDemoApp(appId: string): boolean {
+  return appId in DEMO_EXTERNAL_URLS || appId in DEMO_MOCK_UI
+}
+
+/** Resolve the demo launch URL for an app, or null if it isn't demoable. */
+export function demoAppUrl(appId: string): string | null {
+  return DEMO_EXTERNAL_URLS[appId] ?? DEMO_MOCK_UI[appId] ?? null
+}