fix: enforced global visible_skills in llm node validation and improved skill loading error handling across the project

src/config/paths.rs

@@ -289,6 +289,17 @@ pub fn has_skill(name: &str) -> bool {
     skill_file(name).is_file()
 }
 
+pub fn list_visible_skills(visible: Option<&[String]>) -> Vec<String> {
+    let installed = list_skills();
+    match visible {
+        None => installed,
+        Some(allow) => installed
+            .into_iter()
+            .filter(|name| allow.iter().any(|v| v == name))
+            .collect(),
+    }
+}
+
 pub fn local_models_override() -> Result<Vec<ProviderModels>> {
     let model_override_path = models_override_file();
     let err = || {