feat: add single-donut Binary story and story tests for donut-binary

[c-lamoureux]

Description

Follow-up from reviewing #888:

• Adds a Binary story alongside the existing two-chart Boolean example: a single <Donut isBoolean> using the normal (default) categorical color scheme, matching the design mock (88.3% "Satisfied", pink categorical-600 primary). Proves the secondary-gray override in feat: s2 donut binary #888 works standalone, without requiring a second donut or explicit color overrides.
• Adds DonutBinary.test.tsx, following the existing Donut.test.tsx pattern (render the story, assert on rendered marks/text), covering:
  • Boolean: each chart's primary segment keeps its explicit color; secondary segment is forced to secondary-gray in both charts.
  • Binary: primary segment renders via the normal color scale; secondary segment is still forced to secondary-gray; center-hole value and label render correctly.

Notes

• isBoolean's summary value format is hardcoded to .0% (0 decimals) in donutSummaryUtils.ts, so 0.883 renders as 88%, not 88.3% as in the design mock. The Binary test asserts the actual current behavior (88%). This predates this PR (and feat: s2 donut binary #888) and isn't fixed here — separate from numberFormat, which is already threaded through for the non-boolean summary path but not the boolean one. Worth a follow-up issue.

How Has This Been Tested?

• yarn test --testPathPattern="DonutBinary" — 6/6 passing
• Verified visually in Storybook (Donut/Features/Binary and Boolean)