feat: add socket.dev-sfw-free feature

[Copilot]

Adds a new devcontainer feature for Socket Firewall Free (sfw) — a zero-config network security proxy that blocks malicious dependencies at install time.

Changes

• src/socket.dev-sfw-free/ — New feature: downloads the pre-compiled sfw binary directly from GitHub releases via curl (not npm install -g), supporting amd64 and arm64 Linux targets
  • Asset naming: sfw-free-linux-x86_64 / sfw-free-linux-arm64
  • Binary placed at /usr/local/bin/sfw
• test/socket.dev-sfw-free/test.sh — Verifies sfw --help executes successfully
• README.md — Added to feature table (alphabetically between smallstep.com and sshd), install method: gh release

Usage

"features": {
  "ghcr.io/devcontainer-community/features/socket.dev-sfw-free:1": {}
}

sfw npm install
sfw pip install requests

Original prompt

---

This section details on the original issue you should resolve

<issue_title>create socket.dev/sfw-free feature (id socket.dev-sfw-free)</issue_title>
<issue_description>Use curl install method described here: https://github.com/SocketDev/sfw-free/tree/main
do not use npm install -g</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes create socket.dev/sfw-free feature (id socket.dev-sfw-free) #197

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