Name and order the terminal client code

Name and order the terminal client code

Every package-level name of the terminal client starts with terminal,
and its file is terminal.go, with its tests in terminal_test.go. The
client runs the command "onechat chat", but in the code the chat is the
chat of the agent, with its log, tree, and views, so the prefix names
the client by its kind.

The stop command is in stop.go and the test buffer in buffer_test.go,
because the terminal client and the Telegram bot use them both. The
declarations of the terminal files follow the order of the go-code
skill. The behavior does not change.

Issue: 947bddb