docker-buildx-stale-rust-binary

@divinevideo

Fix deployed Rust binaries not reflecting code changes when using docker buildx. Use when: (1) Code changes are verified locally (tests pass) but production behavior doesn't change after deploy, (2) Docker image has a new tag but contains old compiled binary, (3) Dockerfile uses multi-stage build with dependency pre-compilation layer and source copy layer. Docker buildx layer caching can serve stale compilation output even when source files change, especially with cross-compilation (--platform linux/amd64).