Assistant ignores OS system proxy (manual/PAC) for LLM traffic

Problem

The assistant server's outbound LLM calls do not follow the OS system proxy. Bun/Node do not read the Windows proxy settings (registry ProxyServer/ProxyOverride/AutoConfigURL) or PAC configuration, so on corporate networks — notably Windows with a manual proxy or a setup-script PAC — the agent cannot reach any LLM provider.

Related: #1240 (proxy needed to reach LLM servers on restricted networks).

What would help

• Honor HTTP(S)_PROXY/NO_PROXY env vars for LLM traffic
• Follow the Windows system proxy: manual entries and PAC evaluation
• Keep local providers (Ollama/LMStudio on loopback) direct
• Fail open to direct when no proxy is configured

No proxy auth required for the common case.