- Implement proper brand account detection and switching
- Add getAvailableChannels() to list all accounts (personal + brand)
- Add switchToChannel() with session context injection for brand accounts
- Update cookie authentication instructions for brand account usage
- Add interactive account selection when TARGET_CHANNEL not specified
- Fix account switching by injecting pageId into session context
- Add verification and debugging output for account switching
This allows users to migrate playlists to their YouTube brand accounts,
not just their personal Google accounts.
