[Feature] Support loading environment variable from config file (eg: $HOME/.antigravity/.env) while launching via VSCode extension

Currently, I am using Antigravity VS Code extension in an internal network server, so I have to proxy Antigravity’s traffic to localhost to retrieve subscription information.

Then, I discovered that Antigravity fails to load environment variables from a configuration file; whereas the Codex CLI is able to read environment variables from `$HOME/.codex/.env`.

Perhaps antigravity should also support loading environment variables from a configuration file.