Most of the command-line contract was already tested through run. This
adds what was missing: report and trees with no database exit 1 with
the message telling the user to run scan; a scan that skips an
unreadable file prints its warning and counts the skip in its summary;
the report and trees summary lines are checked exactly. The scan tests
now capture the process's own stdout, which scan would write to
directly, so a stray stdout write in scan fails them. The fatal-path
test takes its subcommands from the command tree, so a new subcommand
wired without runE fails it. The nonexistent-operand test gets an
accurate name.
Model: opus-5-5
sneak