added a dev container

this is to make testing the backend more consistent with the actual runtime environment

.devcontainer/Dockerfile

@@ -0,0 +1,8 @@
+FROM mcr.microsoft.com/devcontainers/javascript-node:20-bookworm
+
+# RUN apt-get update && \
+#  export DEBIAN_FRONTEND=noninteractive && \
+#  apt-get install -y pandoc texlive
+# ^^^ that's a surprise tool that will help us later ^^^
+
+RUN npm install