simplify host fallback logic and fix order

- move decision logic for freeBSD HOST environment var into temp var
- change prioritization from most specific config to least specific,
  meaning that args.host takes precedent over env.HOST, which takes
  precendent over env.UPTIME_KUMA_HOST with no fallback value

server/server.js

@@ -63,12 +63,9 @@ console.info("Version: " + checkVersion.version);
 
 // If host is omitted, the server will accept connections on the unspecified IPv6 address (::) when IPv6 is available and the unspecified IPv4 address (0.0.0.0) otherwise.
 // Dual-stack support for (::)
-let hostname = process.env.UPTIME_KUMA_HOST || args.host;
-
 // Also read HOST if not FreeBSD, as HOST is a system environment variable in FreeBSD
-if (!hostname && !FBSD) {
-    hostname = process.env.HOST;
-}
+let hostEnv = FBSD ? null : process.env.HOST;
+let hostname = args.host || hostEnv || process.env.UPTIME_KUMA_HOST;
 
 if (hostname) {
     console.log("Custom hostname: " + hostname);