Name and order the daemon and socket code

Every package-level name that only the daemon uses starts with daemon:
its hub of socket clients is DaemonHub, a connected client is
DaemonClient, and the loop that serves the agent is daemonServe. So a
client of the socket does not read as the model client or the Bot API
client.

What the daemon and the terminal client share is in socket.go: the
socket file, the size limits, the request type SocketRequest, and the
check of the socket path. The file locks that the log, the daemon, the
login, and the probe share are in lock.go, with their test in
lock_test.go. The declarations of these files follow the order of the
go-code skill. The behavior does not change.

Issue: 947bddb