fix(dashboard): opaque background on ChecklistDropdown popover
The dropdown used bg-[hsl(var(--surface-overlay))] but the CSS variable holds a HEX value (#ffffff / #323752), not HSL components. hsl(#ffffff) is invalid CSS so the background rendered transparent. Switched to inline style with var(--surface-overlay) directly.
Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com