Replace Recharts ScatterChart with compact SVG grid of small rounded squares (11x11px, 2px gap). 7 rows (Mon-Sun) x 24 columns (hours). Color intensity = value relative to max. Transactions = blue scale, Errors = red scale. Toggle switches between modes. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>