fix: remove unused digest field from Settings struct

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/meta_plugin/hostname.rs

@@ -81,7 +81,7 @@ impl HostnameMetaPlugin {
             
             // If no reverse lookup worked, but we have addresses, try to construct FQDN
             // from the first address's domain if the short hostname is part of a domain
-            if let Some(first_addr) = addrs.first() {
+            if let Some(_first_addr) = addrs.first() {
                 // For local addresses, we might not get a reverse lookup, so try to infer
                 // from the system's domain name
                 if let Ok(domain) = std::process::Command::new("domainname").output() {