Restore radar tooltip indicator indexes for valueFormatter

Radar tooltips render one name-value block per indicator, but those blocks did not carry their indicator position into the tooltip markup. Since valueFormatter receives the fragment dataIndex, the callback saw undefined for each radar indicator even though the hovered series data index was known.

The fix keeps the generic tooltip pipeline unchanged and sets dataIndex on radar indicator fragments only. A unit regression covers the formatted markup callback path, and the manual HTML tooltip case makes the indicator-index behavior visible in the existing valueFormatter demo.

Constraint: Existing tooltipMarkup already passes fragment.dataIndex to valueFormatter.

Rejected: Change tooltipMarkup to infer array positions | would broaden behavior for all chart types and duplicate radar-specific knowledge.

Confidence: high

Scope-risk: narrow

Directive: Keep radar indicator indexes scoped to the indicator nameValue fragments; do not replace them with the hovered series dataIndex.

Tested: npx jest --config test/ut/jest.config.cjs --coverage=false test/ut/spec/component/tooltip/tooltip.test.ts

Tested: npm run checktype

Tested: npm run lint

Not-tested: Full browser visual suite