Replace all team_id/team_admin references with account_id/owner across
types, store, hooks, API clients, components, and pages. Add new
AccountSettingsPage, UpgradePrompt, CheckoutButton, useSubscription
hook, and accounts API client. AuthStore now parallel-fetches account
and subscription data alongside user profile.
Also fix folder sidebar not refreshing after tree deletion by
dispatching the folder-changed event in handleDeleteTree.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>