feat(store): coordinate without flock

Target chains, the queue, pushes, the index, the operation log and the compactor take flocks, which only coordinate processes on one machine.

Target heads, change heads, the queue and the compactor become compare-and-swap operations on the storage boundary. "One authority node" becomes "one authority key, any number of processes": two processes that try to append the same acceptance race on the swap, and one loses.