Simplify client proxy port handling

src/server/config.js

@@ -1,14 +1,27 @@
 import path from "node:path";
 
 const dataDir = process.env.DATA_DIR || path.resolve(".vpn-proxy");
+const parsePort = (value, fallback) => {
+  const parsed = Number.parseInt(value, 10);
+  return Number.isInteger(parsed) ? parsed : fallback;
+};
+const proxyPort = parsePort(process.env.PROXY_PORT, 8080);
+const clientProxyPortStart = parsePort(
+  process.env.CLIENT_PROXY_PORT_START,
+  proxyPort,
+);
+const clientProxyPortEnd = parsePort(
+  process.env.CLIENT_PROXY_PORT_END,
+  clientProxyPortStart,
+);
 
 export const settings = {
   appMode: process.env.APP_MODE === "client" ? "client" : "gateway",
-  port: Number(process.env.PORT || 3456),
-  proxyPort: Number(process.env.PROXY_PORT || 8080),
-  clientProxyPortStart: Number(process.env.CLIENT_PROXY_PORT_START || 8080),
-  clientProxyPortEnd: Number(process.env.CLIENT_PROXY_PORT_END || 8090),
-  tproxyPort: Number(process.env.TPROXY_PORT || 7895),
+  port: parsePort(process.env.PORT, 3456),
+  proxyPort,
+  clientProxyPortStart,
+  clientProxyPortEnd,
+  tproxyPort: parsePort(process.env.TPROXY_PORT, 7895),
   tproxyChain: process.env.TPROXY_CHAIN || "VPN_PROXY_TPROXY",
   tproxySourceBypassChain:
     process.env.TPROXY_SOURCE_BYPASS_CHAIN || "VPN_PROXY_SRC_BYPASS",