Remove deprecated #[axum::async_trait] from 2 middleware files (native async traits on Rust 1.88+). Fix 71 stub handlers: change return type from ApiResult<impl IntoResponse> to ApiResult<Json<Value>> and replace todo!() with proper JSON stub responses. Clean compile, zero errors. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>