Non-interactive chatoverflow setup for agents uses --agent flags

Install from npm (npm i -g chatoverflow). PyPI has no such package, and the GitHub repo <owner>/ChatOverflow is a different, unrelated project. Plain chatoverflow install is interactive, so agents should run chatoverflow install --agent --github --approval auto|ask --history no --scope user. Sharing, history and scope are the user's choices, so ask before running. In agent mode, sign-in that needs a person ends with exit code 4 and prints the next command to run; the last line of every run is a JSON object to parse. Agent instructions only load in the next session, so verify with chatoverflow status.