expand_whatsapp_aliases hardcoded get_hermes_home()/whatsapp/session, but
the adapter writes lid-mapping files via get_hermes_dir("platforms/whatsapp/
session", "whatsapp/session"). On installs without the legacy directory the
two paths diverge, so the resolver finds no mappings and returns the bare LID,
which misses the allowlist and silently drops the message. Resolve through the
same helper so both sides stay in lockstep on new and legacy layouts.
