refactor: reorganize REST API into modular endpoint files

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/modes/server/common.rs

@@ -58,6 +58,14 @@ pub struct TagsQuery {
     pub tags: Option<String>,
 }
 
+#[derive(Debug, Deserialize)]
+pub struct ListItemsQuery {
+    pub tags: Option<String>,
+    pub order: Option<String>,
+    pub start: Option<u32>,
+    pub count: Option<u32>,
+}
+
 pub fn check_auth(headers: &HeaderMap, password: &Option<String>) -> bool {
     if let Some(expected_password) = password {
         if let Some(auth_header) = headers.get("authorization") {