agent-browser orphan cleanup

Find and remove Chrome trees that agent-browser launched and then lost track of, and stop them accumulating again.

Symptom

• Hundreds of chrome.exe processes, gigabytes of working set, on an otherwise idle machine.
• agent-browser close --all says ✓ Closed session: default and the processes keep running.
• %TEMP% filling with agent-browser-chrome-<guid> profile directories.

Why it happens

agent-browser launches Chrome and waits for it to write DevToolsActivePort into the profile directory. If that wait times out it reports: