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
Mario Zechner