C2(jobsync): impl — add /tmp and /data directories to nix container

Prisma's get-platform module requires /tmp for temp files. Nix
containers don't create standard directories by default.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

containers/jobsync/default.nix

@@ -113,6 +113,11 @@ pkgs.dockerTools.buildLayeredImage {
     pkgs.coreutils
   ];
 
+  # Create writable directories that don't exist in nix containers
+  extraCommands = ''
+    mkdir -p tmp data
+  '';
+
   config = {
     Entrypoint = [ "${entrypoint}" ];
     WorkingDir = "${jobsync}/app";