fix(proxy): honor HTTP(S)_PROXY when downloading media

[andersonlemesc]

Problem

On a host with no direct internet egress, where all outbound HTTP(S) traffic has to go through a proxy, every incoming media message fails to download. The webhook is delivered with hasMedia: true and media.url: null, and the logs show:

MediaManager: fetch failed: Client network socket disconnected before secure TLS connection was established
  at getHttpStream (@adiwajshing/baileys/lib/Utils/messages-media.js:298)
  ... Failed to execute 'Fetching media', tried '5' times

WHATSAPP_PROXY_SERVER does not cover this: it builds an HttpsProxyAgent for the Baileys socket, while media is fetched through Node's global fetch, which uses undici and ignores that agent.

Node's NODE_USE_ENV_PROXY=1 does not help either, because src/main.ts replaces the global dispatcher during bootstrap:

setGlobalDispatcher(new Agent({ connect: { family: 4 } }));

That call discards the proxy-aware dispatcher installed from the environment, so fetch goes out direct and fails.

Fix

Keep the IPv4 pinning, but pick a proxy-aware dispatcher when proxy variables are present. EnvHttpProxyAgent (undici >= 6.20, and this repo is on ^7.16) reads http_proxy/https_proxy and honors NO_PROXY, so internal hosts such as S3 storage and webhook targets keep going direct.

With no proxy variables set, behavior is identical to today.

Testing

Verified on a proxy-only network with the NOWEB engine: without the change every media download fails with the error above; with it, MediaManager logs The media from '<id>' has been saved. and the webhook carries a working media.url. S3 uploads to an internal endpoint listed in NO_PROXY still go direct.