Add Axum Clean Demo to project showcase (#3371)

Author: sukjaelee

ECOSYSTEM.md

@@ -99,6 +99,7 @@ If your project isn't listed here and you would like it to be, please feel free
 - [Hatsu](https://github.com/importantimport/hatsu): 🩵 Self-hosted & Fully-automated ActivityPub Bridge for Static Sites.
 - [Mini RPS](https://github.com/marcodpt/minirps): Mini reverse proxy server, HTTPS, CORS, static file hosting and template engine (minijinja).
 - [fx](https://github.com/rikhuijzer/fx): A (micro)blogging server that you can self-host.
+- [clean_axum_demo](https://github.com/sukjaelee/clean_axum_demo): A modern, clean-architecture Rust API server template built with Axum and SQLx. It incorporates domain-driven design, repository patterns, JWT authentication, file uploads, Swagger documentation, OpenTelemetry.
 
 [Realworld]: https://github.com/gothinkster/realworld
 [SQLx]: https://github.com/launchbadge/sqlx