Add FETCH_PROXY environment variable for CLI

[Copilot]

• Add support for FETCH_PROXY environment variable in CLI (src/server.js)
  • Read FETCH_PROXY environment variable
  • When FETCH_PROXY is set, use it for both httpProxy and httpsProxy
  • Update validation logic to accept FETCH_PROXY as an alternative to http_proxy/https_proxy
• Update README.md to document FETCH_PROXY
• Manually test FETCH_PROXY behavior
• Run all tests to ensure changes don't break existing functionality (30/30 tests pass)
• Run linter and formatter (no issues)
• Address code review feedback
  • Rename FETCH_PROXY_URI to FETCH_PROXY per maintainer request
  • Revert unrelated changes to javascript.instructions.md

Summary

Successfully implemented the FETCH_PROXY environment variable for the CLI and addressed all code review feedback. The variable supersedes both http_proxy and https_proxy when set, allowing users to configure a single proxy URI for both HTTP and HTTPS requests.

Original prompt

Add a new environment variable to the command line, FETCH_PROXY_URI. When specified, this supercedes both http_proxy and https_proxy, allowing users to configure the proxy just for the fetch request rather than the whole process. We don't need to change createApp, this is just a feature for the CLI.

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[nzakas]

@copilot actually, let's call it FETCH_PROXY instead of FETCH_PROXY_URI

[Copilot]

@copilot actually, let's call it FETCH_PROXY instead of FETCH_PROXY_URI

Renamed to FETCH_PROXY in commit 270a602. Updated both the code and documentation.

[nzakas]

@copilot Revert changes in this file.

[Copilot]

Reverted changes to javascript.instructions.md in commit a6acb32. The file has been restored to its original state.