[runabol]

• Fix a race when tearing down Docker follow log streams in Wait() and probeContainer(): a background io.Copy could still be reading while the log reader (and underlying connection) was closed, which spammed error reading the std out in prod even when tasks succeeded.
• Replace fire-and-forget log copy + immediate defer Close with streamLogs(), which closes the reader, waits for the copy goroutine, and only logs unexpected read errors.
• Treat expected shutdown errors as benign (net.ErrClosed, http.ErrBodyReadAfterClose, http: read on closed response body, etc.). Prod logs showed e.g. read unix @->/run/docker.sock: use of closed network connection — normal teardown of the Moby client socket during log-follow shutdown, not task failure.