Playground demo: the agent-harness approval gate.

Triggers an approval_requested for a risky action (a file delete plus a shell command, marked irreversible) and exercises Raxol.UI.Components.Harness.ApprovalPrompt end to end: blast-radius preview with the IRREVERSIBLE marker, arrow/number-key navigation across the four scope options, and the emitted approval_decision command once the user confirms with Enter.