platform.ts and platform-api.ts both created PlatformClient instances.
Merge all typed helpers (getUserSettings, updateUserSettings,
listSessions, revokeSession, updateProfile) into platform.ts and
delete the duplicate file. Use lazy singleton instead of eager.
feature-flags.ts and prompt-client.ts used bare 'access_token' key
instead of PRODUCT_ID-prefixed key — auth tokens were never sent.
Consolidates 10 web lib files to import the shared getAccessToken()
from api-helpers.ts instead of each redefining their own copy.