The gauge rendered as multiple black rings. Two causes:
1. recharts RadialBarChart draws each data entry as a CONCENTRIC RING, not an
arc segment, so the 3 "track band" entries + value produced 4 nested rings.
Render a single value arc over a neutral background track instead, colored
by status, with the readout absolutely centered (replacing the -mt-12 hack).
2. The fills used hsl(var(--primary)) / hsl(var(--chart-1)) etc., but this
project's Tailwind v4 theme (index.css) defines colors as --color-* holding
full hex values (--color-primary: #4f8cff). So the references were doubly
invalid (wrong name + hsl() wrapping a hex) -> invalid SVG fill defaults to
black. Use var(--color-*) directly, with the semantically correct chart
colors: ok=--color-chart-2 (green), warn=--color-chart-3 (amber),
crit=--color-chart-4 (red).
Also fix the same hsl(var(--x)) -> var(--color-x) bug in LineSeriesChart's
tooltip contentStyle (popover/border/popover-foreground). The line stroke
palette already used the correct var(--color-chart-N) form.
166/166 frontend tests pass; typecheck + ESLint clean.
Developer
50c0c9b548