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

.devcontainer/devcontainer.json

@@ -0,0 +1,13 @@
+{
+  "build": { "dockerfile": "Dockerfile" },
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "esbenp.prettier-vscode",
+        "streetsidesoftware.code-spell-checker",
+        "svelte.svelte-vscode"
+      ]
+    }
+  },
+  "forwardPorts": [5173]
+}