feat: separate Public IP for DNS records from Server IP, improve settings help texts

- Add public_ip field to Settings for DNS A records (proxy/load balancer IP)
- DNS records now use public_ip, falling back to server_ip if empty
- Server IP renamed to "Server IP (Docker Host)" for clarity
- Public IP labeled "Public IP (DNS Target)"
- Updated help texts for domain, server IP, public IP, and Docker network
- DB migration + schema for public_ip column

web/src/lib/i18n/en.json

@@ -287,11 +287,13 @@
     "title": "General Settings",
     "globalConfig": "Global Configuration",
     "domain": "Domain",
-    "domainHelp": "Base domain for subdomain routing",
-    "serverIp": "Server IP",
-    "serverIpHelp": "Public IP address of the server",
+    "domainHelp": "Base domain for subdomain routing (e.g., example.com → stage-dev-app.example.com)",
+    "serverIp": "Server IP (Docker Host)",
+    "serverIpHelp": "IP of the machine running Docker. Used for NPM remote forwarding.",
+    "publicIp": "Public IP (DNS Target)",
+    "publicIpHelp": "IP for DNS A records — typically your proxy/load balancer. Falls back to Server IP if empty.",
     "dockerNetwork": "Docker Network",
-    "dockerNetworkHelp": "Docker network for deployed containers",
+    "dockerNetworkHelp": "Docker network that containers and proxy share. Must match your NPM/Traefik network.",
     "subdomainPattern": "Subdomain Pattern",
     "subdomainPatternHelp": "Pattern for auto-generated subdomains",
     "subdomainVarsTitle": "Available variables",