The trends grid lost its disk chart; add it back as a 6th card plotting
root-filesystem % over time, alongside CPU/Memory/Network/Load/Swap. The
'disk' history series and metric-detail entry already existed, so the
expand-to-detail flow works unchanged.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Signed-off-by: librelad <librelad@digitalangels.vip>