Add devcontainer with Node.js 22 and Bun

Installs dependencies for both root and example/ on container creation.

Co-authored-by: Ona <no-reply@ona.com>

.devcontainer/Dockerfile

@@ -0,0 +1,6 @@
+FROM mcr.microsoft.com/devcontainers/base:ubuntu-24.04
+
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends \
+       curl unzip git ca-certificates \
+    && rm -rf /var/lib/apt/lists/*