fix(ai,coding-agent): make pi-ai browser-safe and move OAuth runtime exports

- add browser smoke bundling check to root check + pre-commit

- lazy-load Bedrock provider registration to avoid browser graph traversal

- remove top-level OAuth runtime exports from @mariozechner/pi-ai

- add @mariozechner/pi-ai/oauth subpath export and update coding-agent imports

- move proxy dispatcher init to coding-agent CLI (Node-only)

- document Bedrock/OAuth browser limitations

closes #1814

packages/coding-agent/src/cli.ts

@@ -7,6 +7,9 @@
  */
 process.title = "pi";
 
+import { EnvHttpProxyAgent, setGlobalDispatcher } from "undici";
 import { main } from "./main.js";
 
+setGlobalDispatcher(new EnvHttpProxyAgent());
+
 main(process.argv.slice(2));