On a pipe, a file or /dev/null each scan phase now prints its zero-state
line the moment it starts instead of after its first finished item, so
a slow first read under cron no longer leaves the log silent. Terminal
detection uses golang.org/x/term, now a direct dependency listed in the
README; the old character-device test took /dev/null for a terminal.
The walk spinner no longer redraws from the library's own goroutine; it
advances only as items complete, so a redraw cannot garble a warning.
Building the bar moved into newBar so the terminal display can be
tested without a terminal.
Lint suppressed: gosec on two test file opens, paralleltest on three
tests that replace os.Stderr.
Model: opus-5-5
