Refactor OAuth/API key handling: AuthStorage and ModelRegistry

- Add AuthStorage class for credential storage (auth.json)
- Add ModelRegistry class for model management with API key resolution
- Add discoverAuthStorage() and discoverModels() discovery functions
- Add migration from legacy oauth.json and settings.json apiKeys to auth.json
- Remove configureOAuthStorage, defaultGetApiKey, findModel, discoverAvailableModels
- Remove apiKeys from Settings type and SettingsManager methods
- Rename getOAuthPath to getAuthPath
- Update SDK, examples, docs, tests, and mom package

Fixes #296

tsconfig.json

@@ -28,5 +28,5 @@
 		}
 	},
 	"include": ["packages/*/src/**/*", "packages/*/test/**/*", "packages/coding-agent/examples/**/*"],
-	"exclude": ["packages/web-ui/**/*"]
+	"exclude": ["packages/web-ui/**/*", "**/dist/**"]
 }