Web Bluetooth only reveals services you ask for up front, so list every candidate below
(one per line, 16-bit or 128-bit). After connecting, every matching service and its characteristics are
listed. Subscribe to a notify characteristic to watch the raw data stream — you should see
EM,1,… arriving in ~20-byte pieces. For a complete, unfiltered view, also check with the
nRF Connect app or chrome://bluetooth-internals.