When SESSION_DIR has no session .json files and the index is empty/absent,
print_startup_config() now scans sibling state directories and prints a diagnostic
pointing the user at the populated sibling + the HERMES_WEBUI_STATE_DIR to set —
fully fail-safe (try/except, warning-only, no behavior change).
Closes#3915.
Co-authored-by: Rod Boev <rod.boev@gmail.com>