agent.md: fix the friction a fresh agent hit on its first run

A sub-agent that had only agent.md audited fastapi/typer and listed 14 friction points. This fixes the ones in the doc and the code.

• Windows forms of the preflight and the install (py -3.11, WSL docker, Activate.ps1, PowerShell 7 and UTF-8 redirects).
• doctor retries a network probe once, and its fix text says to rerun. agent.md says when to use --for audit.
• top_tasks can hold fewer than 10 tasks. The summary keys, ancient, UTC ids, absolute paths and the Jev-off meaning of stale are named.
• doctor names the env file it read.