WIP: Remove global state from pi-ai OAuth/API key handling

- Remove setApiKey, resolveApiKey, and global apiKeys Map from stream.ts
- Rename getApiKey to getApiKeyFromEnv (only checks env vars)
- Remove OAuth storage layer (storage.ts deleted)
- OAuth login/refresh functions now return credentials instead of saving
- getOAuthApiKey/refreshOAuthToken now take credentials as params
- Add test/oauth.ts helper for ai package tests
- Simplify root npm run check (single biome + tsgo pass)
- Remove redundant check scripts from most packages
- Add web-ui and coding-agent examples to biome/tsgo includes

coding-agent still has compile errors - needs refactoring for new API

packages/coding-agent/examples/sdk/02-custom-model.ts

@@ -4,7 +4,7 @@
  * Shows how to select a specific model and thinking level.
  */
 
-import { createAgentSession, findModel, discoverAvailableModels } from "../../src/index.js";
+import { createAgentSession, discoverAvailableModels, findModel } from "../../src/index.js";
 
 // Option 1: Find a specific model by provider/id
 const { model: sonnet } = findModel("anthropic", "claude-sonnet-4-20250514");