fix: resolve clippy warnings and test errors

- Implement FromStr trait for NodeType instead of custom from_str method
- Fix redundant_closure warning in server.rs:455
- Add #[allow(clippy::too_many_arguments)] for new_file_node
- Fix unused variables in tests (_user_id, _conn)
- Remove unused imports (NodeType, serde_json::json)
- Replace len() > 0 with !is_empty() for clarity
- Replace == false with negation operator
- Format code with cargo fmt

tests/api_logic_test.rs

@@ -4,7 +4,6 @@
 use markbase::filetree::node::NodeType;
 use markbase::filetree::{mode, FileTree};
 use rusqlite::Connection;
-use serde_json::json;
 use uuid::Uuid;
 
 fn temp_db() -> (Connection, String) {
@@ -213,7 +212,7 @@ fn test_api_logic_get_modes() {
 
 #[test]
 fn test_api_logic_file_info() {
-    let (conn, user_id) = temp_db();
+    let (conn, _user_id) = temp_db();
 
     let file_uuid = "test_file_uuid_123";
     FileTree::add_location(&conn, file_uuid, "/path/to/file.mp4", Some("origin")).unwrap();