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/07-context-files.ts

@@ -14,7 +14,7 @@ for (const file of discovered) {
 }
 
 // Use custom context files
-const { session } = await createAgentSession({
+await createAgentSession({
 	contextFiles: [
 		...discovered,
 		{