Update xpower-flow-card.js

v1.3.29
   - Battery 24h graph now uses net charge/discharge when split
     battery_charge / battery_discharge entities are configured,
     instead of only the single battery power sensor (fixes a flat
     or empty battery sparkline on Growatt and similar split setups).
   - Trend arrows redesigned: crisp SVG chevrons beside each value,
     coloured per node, animate on value change (honours reduced
     motion). New option arrow_style: chevron (default) | arrow.

Author: BTNBx