Add tests for proxy request forwarding, authentication, and error handling

[KochC]

Problem

All three existing tests cover only CORS headers. The core proxy behaviour — request forwarding to upstream, authentication token validation, and error responses — has no test coverage.

Why now

Any change to index.js request-handling logic can silently break auth or forwarding with no CI signal.

Acceptance criteria

• Test: valid auth token results in proxied request to upstream
• Test: missing or invalid auth token returns HTTP 401
• Test: upstream timeout or error returns HTTP 502
• Test: malformed JSON body returns HTTP 400
• All new tests pass in npm test

Target files

• index.test.js
• index.js

Suggested validation

• npm test passes with all new cases
• Each test asserts a specific status code and response body

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Created by autobot — risk: low