Add custom service log file support with L key

- Add ServiceLogConfig structure for per-host service log paths
- Implement L key handler for custom log file viewing via tmux popup
- Update dashboard config to support service_logs HashMap
- Add tail -f command execution over SSH for real-time log streaming
- Update status line to show L: Custom shortcut
- Document configuration format in CLAUDE.md

Each service can now have custom log file paths configured per host,
accessible via L key with same tmux popup interface as journalctl.

dashboard/src/ui/mod.rs

@@ -308,6 +308,34 @@ ssh -tt {}@{} 'bash -ic {}'",
                             .ok(); // Ignore errors, tmux will handle them
                     }
                 }
+                KeyCode::Char('L') => {
+                    // Show custom service log file in tmux popup
+                    if let (Some(service_name), Some(hostname)) = (self.get_selected_service(), self.current_host.clone()) {
+                        // Check if this service has a custom log file configured
+                        if let Some(host_logs) = self.config.service_logs.get(&hostname) {
+                            if let Some(log_config) = host_logs.iter().find(|config| config.service_name == service_name) {
+                                let tail_command = format!(
+                                    "ssh -tt {}@{} 'tail -f {}'",
+                                    self.config.ssh.rebuild_user,
+                                    hostname,
+                                    log_config.log_file_path
+                                );
+                                
+                                std::process::Command::new("tmux")
+                                    .arg("display-popup")
+                                    .arg("-w")
+                                    .arg("80%")
+                                    .arg("-h") 
+                                    .arg("80%")
+                                    .arg("-T")
+                                    .arg(format!("Custom Log: {}", service_name))
+                                    .arg(&tail_command)
+                                    .spawn()
+                                    .ok(); // Ignore errors, tmux will handle them
+                            }
+                        }
+                    }
+                }
                 KeyCode::Char('b') => {
                     // Trigger backup
                     if let Some(hostname) = self.current_host.clone() {
@@ -718,6 +746,7 @@ ssh -tt {}@{} 'bash -ic {}'",
         shortcuts.push("r: Rebuild".to_string());
         shortcuts.push("s/S: Start/Stop".to_string());
         shortcuts.push("J: Logs".to_string());
+        shortcuts.push("L: Custom".to_string());
         
         // Always show quit
         shortcuts.push("q: Quit".to_string());