Announce the pauses state in the three build modules, and pin mesh-sdk 518dae5 (an unreadable pause pulls as not paused)

Without it in Kept, stdio.KeptState refuses the state before the bus (mesh-sdk go/keeps.go
refusedUnannounced), so the pause could be neither read nor written.

modules/mesh-build-node/cmd/mesh-build-node/announce.go

@@ -14,6 +14,7 @@ var Kept = []announce.State{
 	{Name: "toolchains", Readable: true},
 	{Name: "keys", Readable: true},
 	{Name: "steps", Readable: true},
+	{Name: "pauses", Readable: true},
 }
 
 // keepStates announces Kept as this module's (stdio.Keeps): main calls it before it serves.