feat(misc): add human-in-the-loop approval notebook for irreversible actions

Implements IrreversibleActionGate: classifies reversibility via tool-use,
runs dry-run preflight, renders structured approval request with blast
radius, and applies asyncio.wait_for timeout-abort (silence=abort).
Three examples: bulk email, DB delete, prod deploy.

Closes #701

Author: RudrenduPaul