Add devcontainer configuration for TypeScript-Node

This sets up a dev container using a TypeScript-Node image. It includes a spell checker extension, forwards port 4321, and runs `npm install` after setup to ensure dependencies are installed.

Author: maartenba

.devcontainer.json

@@ -0,0 +1,15 @@
+{
+  "image": "mcr.microsoft.com/devcontainers/typescript-node:22",
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "astro-build.astro-vscode",
+        "esbenp.prettier-vscode"
+      ]
+    }
+  },
+  "forwardPorts": [
+    4321
+  ],
+  "postCreateCommand": "npm install"
+}