feat: Make mcp support an optional feature, disabled by default

Co-authored-by: aider (openai/andrew/openrouter/sonoma-sky-alpha) <aider@aider.chat>

src/modes/server/api/mod.rs

@@ -1,5 +1,6 @@
 pub mod item;
 pub mod status;
+#[cfg(feature = "mcp")]
 pub mod mcp;
 
 use axum::{
@@ -67,6 +68,7 @@ pub fn add_routes(router: Router<AppState>) -> Router<AppState> {
         .route("/api/item/{item_id}/content", get(item::handle_get_item_content))
         
         // MCP endpoints
+        #[cfg(feature = "mcp")]
         .route("/mcp/sse", get(mcp::handle_mcp_sse))
 }