fix(ui): DNS apply no longer blanks the page + WiFi/DNS modals cover the whole app

Applying DNS assigned the RPC response's fields into networkData without
guarding the shape; the demo mock answered {success:true} with no
servers array, dnsServers became undefined, and the dnsDisplayLabel
computed crashed the whole page render on .length. Guard the assignment,
teach the mock to round-trip DNS state per session, and Teleport the
WiFi + DNS modals to body so they overlay the full app instead of just
the right panel (position:fixed is containing-block-relative inside the
dashboard).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/mock-backend.js

@@ -2418,20 +2418,34 @@ app.post('/rpc/v1', (req, res) => {
       }
 
       case 'network.dns-status': {
+        const dns = mockState.dns || { provider: 'system', servers: ['1.1.1.1', '9.9.9.9'], doh_enabled: false }
         return res.json({
           result: {
-            provider: 'system',
-            servers: ['1.1.1.1', '9.9.9.9'],
-            doh_enabled: false,
+            provider: dns.provider,
+            servers: dns.servers,
+            doh_enabled: dns.doh_enabled,
             doh_url: null,
-            resolv_conf_servers: ['1.1.1.1', '9.9.9.9'],
+            resolv_conf_servers: dns.servers,
           },
         })
       }
 
       case 'network.configure-dns': {
-        console.log(`[Network] DNS configured: ${params?.provider}`)
-        return res.json({ result: { success: true } })
+        const dnsProviders = {
+          system: ['192.168.4.1'],
+          cloudflare: ['1.1.1.1', '1.0.0.1'],
+          google: ['8.8.8.8', '8.8.4.4'],
+          quad9: ['9.9.9.9', '149.112.112.112'],
+          mullvad: ['194.242.2.2'],
+        }
+        const provider = params?.provider || 'system'
+        const servers = provider === 'custom'
+          ? (Array.isArray(params?.servers) ? params.servers : [])
+          : (dnsProviders[provider] || dnsProviders.system)
+        const doh_enabled = ['cloudflare', 'google', 'quad9', 'mullvad'].includes(provider)
+        mockState.dns = { provider, servers, doh_enabled }
+        console.log(`[Network] DNS configured: ${provider} → ${servers.join(', ')}`)
+        return res.json({ result: { provider, servers, doh_enabled } })
       }
 
       case 'network.accept-request': {