In Docker the install tree (/opt/hermes) is read-only, so npm install for
the WhatsApp bridge fails with EACCES. Add resolve_whatsapp_bridge_dir() in
whatsapp_common.py: when the install dir is read-only, mirror the bridge
source into a writable HERMES_HOME location and use that. Both the
adapter and the 'hermes whatsapp' CLI resolve through the shared helper so
the install and runtime paths agree.
Fixes#49561
491579fa05