refactor: Consolidate item content filtering into a single filter string

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

src/services/item_service.rs

@@ -139,19 +139,11 @@ impl ItemService {
         &self,
         conn: &Connection,
         id: i64,
-        head_bytes: Option<usize>,
-        head_words: Option<usize>,
-        head_lines: Option<usize>,
-        tail_bytes: Option<usize>,
-        tail_words: Option<usize>,
-        tail_lines: Option<usize>,
-        line_start: Option<usize>,
-        line_end: Option<usize>,
-        grep: Option<String>,
+        filter: Option<String>,
     ) -> Result<(Vec<u8>, String, bool), CoreError> {
         // Use streaming approach to handle all filtering options consistently
         let (mut reader, mime_type, is_binary) = self.get_item_content_info_streaming(
-            conn, id, None
+            conn, id, filter
         )?;
         
         // Read all the filtered content into a buffer