fix: kubeconfig falls back to .kube if KUBECONFIG env variable is not set

harmony/src/domain/topology/k8s_anywhere/k8s_anywhere.rs

@@ -1006,8 +1006,28 @@ impl K8sAnywhereConfig {
     }
 
     fn from_env() -> Self {
+        fn get_kube_config_path() -> Option<std::path::PathBuf> {
+            // 1. Check for the KUBECONFIG environment variable first (standard practice)
+            if let Ok(val) = std::env::var("KUBECONFIG") {
+                if !val.is_empty() {
+                    return Some(std::path::PathBuf::from(val));
+                }
+            }
+
+            // 2. Use the standard library to find the home directory
+            // As of recent Rust versions, this is the preferred cross-platform method.
+            let mut path = std::env::home_dir()?;
+
+            // 3. Construct the path to .kube/config
+            // .push() handles OS-specific separators (\ for Windows, / for Unix)
+            path.push(".kube");
+            path.push("config");
+
+            Some(path)
+        }
+
         Self {
-            kubeconfig: std::env::var("KUBECONFIG").ok().map(|v| v.to_string()),
+            kubeconfig: get_kube_config_path().map(|s| s.to_string_lossy().into_owned()), 
             use_system_kubeconfig: std::env::var("HARMONY_USE_SYSTEM_KUBECONFIG")
                 .map_or_else(|_| false, |v| v.parse().ok().unwrap_or(false)),
             autoinstall: std::env::var("HARMONY_AUTOINSTALL")