refactor: deduplicate ItemInfo, improve error handling, fix pre-existing bugs

- Move ItemInfo to services/types.rs for sharing between client and server
- Replace .expect() in compression_service with proper error handling
- Add CoreError::PayloadTooLarge variant for semantic error handling
- Export CoreError from lib.rs for library users
- Unify get_item_meta_name/value to take &str instead of String
- Extract item_path() helper in ItemService to reduce duplication
- Add warning logs for silent errors in list.rs
- Fix pre-existing borrow errors: tx moved in export handler,
  item_with_meta partial move in TryFrom implementation
- Fix unused data_dir variables in server code

src/lib.rs

@@ -52,6 +52,7 @@ pub mod tokenizer;
 pub use args::Args;
 // Re-export PIPESIZE constant
 pub use common::PIPESIZE;
+pub use services::CoreError;
 
 // Import all filter plugins to ensure they register themselves
 #[allow(unused_imports)]