Approve or reject a change a monitor proposed

Applies or declines one proposal that a monitor created. Approving executes it exactly once against the ad platform and reads the object back; rejecting marks it so it can never execute. Use when: the user has explicitly said yes or no to the specific change — quote its summary from list_pending_actions first. Do not use when: the user is still deciding, or the proposal came from a tool call they made themselves (use approve_proposal / reject_proposal, which say the same thing in that context). Approving is real money: a pause stops delivery, a budget cut changes what the campaign can spend. If the proposal expired or was already decided, this returns an error — say so rather than silently recreating it.