[dmoonventure070-art]

Closes #917

Summary

Fixes the SVG donut geometry in AllocationWidget where slices were rendered with strokeDasharray="${len} ${C}" (period len + C instead of C) and strokeDashoffset={C - cumulative}, shifting each slice by its own length and producing negative dash lengths on tiny slices (< 0.56%).

Changes

• Correct SVG dash period & offset (src/components/AllocationWidget.tsx):
  • Clamp dashLen using Math.max(0, sliceLen - (gap / 360) * circumference) so tiny slices never produce negative dash lengths.
  • Use strokeDasharray={${seg.dashLen} ${circumference - seg.dashLen}} so the dash pattern period is always circumference (C).
  • Use strokeDashoffset={-cumulativeLen} so slice i starts at the cumulative arc length of preceding slices.
• Normalise slice percentages (normaliseSlices):
  • Ensure both the drawn donut arcs and the legend percentages derive from the same normalised data when input totals do not sum to 100.
• Unit & regression tests (src/components/AllocationWidget.test.tsx):
  • Assert computed stroke-dasharray and stroke-dashoffset for [50, 50] (two half rings), [70, 20, 10], and [99.7, 0.3].
  • Verify no negative dash values are produced for sub-gap slices.
  • Verify un-normalised slice totals render matching normalised arcs and legend percentages.

Verification

• npx vitest run src/components/AllocationWidget.test.tsx --coverage (25/25 passing, 100% statement/branch/function/line coverage on AllocationWidget.tsx)
• npm run lint passes with zero warnings/errors