fix(build): perbaiki referensi paket zesdex-gateway di Dockerfile & default.nix

- Dockerfile & default.nix: ganti zesdex-backend -> zesdex-gateway (binary zesdex)
- flake.nix & default.nix: versi 1.13.0 -> 1.18.2 mengikuti Cargo.toml
- chore(ci): drop cargo build --release dari check job, tambah cargo fmt --check

flake.nix

@@ -34,7 +34,7 @@
 
         packages.default = pkgs.rustPlatform.buildRustPackage {
           pname = "zesdex";
-          version = "1.13.0";
+          version = "1.18.2";
           src = ./.;
 
           cargoLock = {