feat(tls): add optional nginx setup and gateway preview

frontend/src/locales/en-US.json

@@ -288,6 +288,7 @@
     "depReady": "✓ Dependencies Ready",
     "notDeployed": "Not Deployed",
     "oneClickInstall": "One-Click Install",
+    "onDemandHint": "Dependencies are checked without installing anything. Choose a protocol, then install only that protocol's missing dependencies from its card.",
     "installCmd": "Install Command",
     "customPlugin": "Custom Protocol Plugin",
     "customScene": "Custom Integration",
@@ -730,11 +731,16 @@
   },
   "tls": {
     "title": "Domain & certificate",
-    "description": "OpsX VPN can serve ports 80/443 with automatic ACME HTTP-01 issuance and renewal; Nginx and Certbot are optional.",
+    "description": "Use OpsX VPN for automatic HTTP-01 certificates or preview an external Nginx / Certbot gateway.",
     "domain": "Configured domain", "activeDomain": "Active domain", "saveDomain": "Save domain", "restartRequired": "Domain saved; restart OpsX VPN to enable ports 80/443 and automatic issuance", "saveFailed": "Could not save domain", "dns": "DNS", "certificate": "Certificate", "valid": "Valid", "pending": "Pending first HTTPS handshake",
     "notConfigured": "Disabled", "saved": "Domain configuration saved", "issuer": "Issuer", "expires": "Expires", "renewal": "Renewal", "automatic": "Automatic (autocert)",
-    "ports": "Listening ports (HTTP / HTTPS)", "setupHint": "Save the domain and restart the server, then allow public TCP 80/443. The first HTTPS request issues a certificate and caches it in data/acme. VPN_TLS_DOMAIN may also be used and overrides the saved setting. Preserve the data directory.",
-    "refresh": "Refresh status", "openHttps": "Open HTTPS health check", "loadFailed": "Could not load certificate status"
+    "ports": "HTTP / HTTPS ports", "externalPorts": "Managed by external Nginx; listener status not checked", "setupHint": "Restart to apply a saved domain or mode. Before switching to Nginx, follow the deployment guide to install it, issue a certificate, and validate the configuration. Go mode caches certificates in data/acme; saving settings alone does not issue a certificate.",
+    "refresh": "Refresh status", "openHttps": "Open HTTPS health check", "loadFailed": "Could not load certificate status",
+    "mode": "Public entry mode", "goMode": "Go automatic certificate (binds 80/443)", "nginxMode": "Nginx proxy (external 80/443)", "saveMode": "Save entry mode",
+    "nginxHint": "Saving this mode does not install or start Nginx. Install Nginx and Certbot, verify issuance, configuration and renewal, then restart OpsX VPN. Go will no longer bind 80/443.",
+    "externalRenewal": "Managed by Certbot (separate deployment required)", "previewNginx": "Preview Nginx configuration", "previewOnly": "Read-only preview; nothing has been installed or enabled. Use HTTP for issuance first, then enable HTTPS after the certificate exists.", "httpSite": "HTTP-01 site", "httpsSite": "HTTPS management site",
+    "setupTitle": "Optional HTTPS public gateway", "setupStepCheck": "Detect system", "setupStepInstall": "Install dependencies", "setupStepConfigure": "Configure gateway and certificate", "detectedSystem": "Server OS", "setupUnsupported": "Automatic setup requires root on Ubuntu or TencentOS Server 4", "setupScope": "Use only if you choose the Nginx gateway. Installs Nginx / Certbot and prepares the validation directory. It does not install VPN protocol dependencies, enable ports, or issue certificates.", "setupButton": "Prepare Nginx / Certbot", "setupComplete": "Dependencies are ready; configure the site and certificate next", "setupFailed": "Initialization failed; inspect the output", "setupInterrupted": "Log connection interrupted; refresh status. Installation may still be running on the server",
+    "commonSetupTitle": "First-time shared network setup", "commonSetupHint": "Check permissions, default route and IPv4 forwarding. Enable shared forwarding only when needed; install protocol-specific dependencies separately in Create Tunnel.", "hostRoot": "Privileges", "hostRoute": "Default route", "hostForward": "IPv4 forwarding", "enableForwarding": "Enable IPv4 forwarding", "forwardingEnabled": "IPv4 forwarding enabled"
   },
   "protocols": {
     "wireguard": {