ask: the control plane calls a module's tool and prints its answer

A module serves tools under an account scoped to exactly that, and nothing else in
the mesh held an account that could ask one. The control plane does: ask publishes
on the RPC exchange with a private reply queue bound under its own name, checks the
correlation, prints the answer, and exits non-zero for a tool that answered with an
error or a module that never answered (novox/hq 04-ISSUES/049, ADR 0095).

cmd/mesh-controller/main.go

@@ -68,6 +68,8 @@ func run() error {
 		return licenceCommand(ctx, args[1:])
 	case "rotate":
 		return rotateCommand(ctx, args[1:])
+	case "ask":
+		return askCommand(ctx, args[1:])
 	case "builds":
 		return buildsCommand(ctx, args[1:])
 	case "pin":
@@ -171,6 +173,7 @@ func usage() {
   licence manager <name> <node>  the node that holds a refreshable licence's refresh token
   licence refresh <name>         mint a new access token and seal it to every holder
   rotate <provision> [--consumer <n>]  a new credential for every holder, both ends at once
+  ask <module> <tool> [json]           call one of a module's tools over the broker, and print its answer
   pin <node> <provision> <from>  which node this one gets a provision from
   unpin <node> <provision>       put that question back
   plan <node> [--files|--json]     what that node would run, and why