fix(ai): OAuth login/refresh now respects HTTP proxy env vars

Extracted HTTP proxy setup to shared module and imported it from both
stream.ts and oauth/index.ts. This ensures fetch() calls during OAuth
flows (token exchange, refresh, project discovery) go through the proxy.

fixes #1132

packages/ai/src/utils/oauth/index.ts

@@ -9,6 +9,9 @@
  * - Antigravity (Gemini 3, Claude, GPT-OSS via Google Cloud)
  */
 
+// Set up HTTP proxy for fetch() calls (respects HTTP_PROXY, HTTPS_PROXY env vars)
+import "../http-proxy.js";
+
 // Anthropic
 export { anthropicOAuthProvider, loginAnthropic, refreshAnthropicToken } from "./anthropic.js";
 // GitHub Copilot