Add option to disable built-in terminal scrolling (for tmux compatibility)

When running Claude Code inside tmux, the CLI captures Page-Up/Page-Down keys for its own scrolling, which prevents tmux's native copy-mode scroll from working. There's currently no way to disable this behavior.

Request: Add a config option (e.g. disableTerminalScrolling: true in settings or an env var) to let the terminal/multiplexer handle scrolling instead.

Workaround today: Use Ctrl+B + Page-Up to invoke tmux copy mode, but this is non-intuitive for users accustomed to native tmux scrolling.