Set Board Agent

Switch the platform's own agent on or off for this app. An app admin's.

Turning an autonomous committer on for someone's repository should be a decision somebody made, not a side effect of opening the board — which is why the agent is not granted access anywhere else, and why this is gated the same way the ticket prefix is.

Deliberately HTTP only, with no MCP twin. The rule that a gate needs both surfaces is about a gate being BYPASSABLE on the one that lacks it; a capability that simply is not exposed over MCP cannot be reached from there at all. It also costs nothing against TOTAL_DESCRIPTION_CEILING, which has single-digit headroom.