feat: replace hardcoded buffer sizes with PIPESIZE constant

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/services/item_service.rs

@@ -1,3 +1,4 @@
+use crate::common::PIPESIZE;
 use crate::config::Settings;
 use crate::services::compression_service::CompressionService;
 use crate::services::error::CoreError;
@@ -274,7 +275,7 @@ impl ItemService {
         
         let mut item_out = compression_engine.create(item_path.clone())?;
         
-        let mut buffer = [0; 8192];
+        let mut buffer = [0; PIPESIZE];
         let mut total_bytes = 0;
 
         debug!("ITEM_SERVICE: Starting to read and process input data");