feat(devcontainer): add Claude Code extension and VS Code marketplace URLs

- Add anthropic.claude-code extension to default extensions list
- Allow VS Code marketplace URLs in firewall configuration:
  - marketplace.visualstudio.com (marketplace API)
  - vscode.blob.core.windows.net (extension downloads)
  - update.code.visualstudio.com (VS Code updates/metadata)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.devcontainer/devcontainer.json

@@ -16,6 +16,7 @@
   "customizations": {
     "vscode": {
       "extensions": [
+        "anthropic.claude-code",
         "dbaeumer.vscode-eslint",
         "esbenp.prettier-vscode",
         "eamodio.gitlens"