Fix: honor HTTPS_PROXY/HTTP_PROXY in proxy-only environments

[zdavis-rollbar]

Summary

• Fixes EAI_AGAIN DNS failures in proxy-only environments (corporate networks, containerized sandboxes, Claude Code remote) where Node.js fetch (undici) silently ignores HTTPS_PROXY/HTTP_PROXY env vars
• Adds undici as an explicit dependency and installs a ProxyAgent as the global fetch dispatcher at startup when any proxy env var is detected (HTTPS_PROXY, HTTP_PROXY, https_proxy, http_proxy)
• No behavior change for users without a proxy configured

Closes #83

How it works

A new src/utils/proxy.ts module is imported at the top of src/index.ts (before any fetch() calls). If a proxy env var is present, it calls setGlobalDispatcher(new ProxyAgent(url)), which makes all subsequent fetch() calls route through the proxy automatically.

undici is added as an explicit npm dependency for Node 20 compatibility — node:undici is only available from Node 22+, and the project targets >=20.

Test plan

• 6 unit tests added in tests/unit/utils/proxy.test.ts covering all four proxy env vars, priority ordering, and the no-proxy case
• Smoke test: HTTPS_PROXY=http://localhost:9999 node build/index.js produces ECONNREFUSED (proxy attempted) rather than EAI_AGAIN (DNS failure) — confirming proxy routing is active
• Full replication: run inside a Docker container with --dns=0.0.0.0 (DNS blocked) and a real proxy on the host — traffic routes through the proxy successfully

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