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/modes/list.rs

@@ -151,13 +151,19 @@ pub fn mode_list(
                     Some(size) => format_size(size as u64, settings.human_readable),
                     None => match item_path.metadata() {
                         Ok(_) => "Unknown".to_string(),
-                        Err(_) => "Missing".to_string(),
+                        Err(e) => {
+                            log::warn!("File missing or inaccessible: {}", e);
+                            "Missing".to_string()
+                        }
                     },
                 },
                 ColumnType::Compression => item.compression.to_string(),
                 ColumnType::FileSize => match item_path.metadata() {
                     Ok(metadata) => format_size(metadata.len(), settings.human_readable),
-                    Err(_) => "Missing".to_string(),
+                    Err(e) => {
+                        log::warn!("File missing or inaccessible: {}", e);
+                        "Missing".to_string()
+                    }
                 },
                 ColumnType::FilePath => item_path
                     .clone()