ensureUserPub only ran os.MkdirAll, so a freshly-provisioned /public
(and thus ~<name>/public on the web) came up empty — only ~chovy had a
README because it was uploaded by hand. Embed that help text as a
default and write it whenever the area has no README.txt.
ensureUserPub is hit on SFTP connect (fs.go) and when the web host
materializes ~<name>/public (AnonRoot), so this self-heals every
existing empty member the next time they connect or their page is
viewed — no manual backfill. A member's own README is never clobbered.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
