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/client.rs

@@ -1,22 +1,9 @@
-use crate::services::error::CoreError;
+use crate::services::{ItemInfo, error::CoreError};
 use base64::Engine;
 use serde::de::DeserializeOwned;
 use std::collections::HashMap;
 use std::io::Read;
 
-/// Item information returned from the server API.
-#[derive(Debug, Clone, serde::Deserialize, serde::Serialize)]
-pub struct ItemInfo {
-    pub id: i64,
-    pub ts: String,
-    pub uncompressed_size: Option<i64>,
-    pub compressed_size: Option<i64>,
-    pub closed: bool,
-    pub compression: String,
-    pub tags: Vec<String>,
-    pub metadata: HashMap<String, String>,
-}
-
 /// Percent-encode a value for use in a URL query string.
 fn url_encode(s: &str) -> String {
     let mut result = String::with_capacity(s.len() * 3);