fix: remove hardcoded Unix $ prompt prefix from terminal UI (#11429)

The terminal command display hardcoded a `$ ` before every command.
This is a Unix shell convention with no meaning on Windows (PowerShell,
cmd) and doesn't reflect the user's actual shell. Since the command is
already visually distinct inside a labeled Terminal block, the prefix
adds no information and is misleading cross-platform.

Closes #11428

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>