The health monitoring widget computed total memory from info.memory.layout[].size
and derived used memory from percentTotal. On some Unraid versions the layout size
is reported in KiB, causing the RAM value to be ~1024x too small (0.01 GiB instead
of ~12 GiB) while the percentage ring stayed correct.
Use metrics.memory.total and metrics.memory.available (documented as bytes) with
used = total - available, matching Unraid's own percentTotal calculation. Removes
the now-unused info.memory.layout query and schema field and adds regression tests.