Devcontainer fails to build on Apple Silicon (arm64) due to trixie base image

The devcontainer fails to build on Apple Silicon Macs. The base image `mcr.microsoft.com/vscode/devcontainers/javascript-node:22` resolves to Debian 13 (trixie) on arm64, where `python3-distutils` and `software-properties-common` are unavailable, causing the `apt-get install` step to fail.

**Verified with:**
```
$ docker run --rm --platform linux/arm64 \
mcr.microsoft.com/vscode/devcontainers/javascript-node:22 \
cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 13 (trixie)"
```

**Error:**
```
E: Unable to locate package software-properties-common
E: Package 'python3-distutils' has no installation candidate
```

**Fix:** Pin the base image in `.devcontainer/Dockerfile` to the bookworm variant:
```dockerfile
FROM mcr.microsoft.com/vscode/devcontainers/javascript-node:22-bookworm
```

This is a one-line change that makes the devcontainer build correctly on arm64.