fix: vlt bar color invisible in dark mode

[vltbaudbot]

Problem

The vlt bar in the bar charts uses black (#000000) as its brand color, which is invisible on dark backgrounds when dark mode is active. This also affected the legend dots, tooltips, and DNF (did not finish) striped patterns for vlt.

Additionally, the component was comparing against theme (which can be "system") instead of resolvedTheme (which resolves to the actual "dark" or "light" preference), meaning users with system-level dark mode preferences wouldn't see the fix.

Fix

• Added getColor() helper that resolves vlt's display color to white in dark mode, used consistently across all chart elements:
  • Bar fills and Cell fills (consolidated chart)
  • Individual per-fixture charts
  • Legend dot colors (chartConfig and individualChartConfig)
  • DNF striped patterns (base color + lightened color)
  • DNF fallback fills in consolidated data
• Replaced all theme === "dark" → resolvedTheme === "dark" (6 occurrences) for axis ticks, labels, and legend wrapper styling so system dark mode is correctly detected
• Updated useMemo dependency arrays to include resolvedTheme where getColor is used, ensuring proper re-rendering on theme changes

Testing

• TypeScript compiles cleanly (tsc -b --noEmit)
• ESLint passes with no warnings