Honor PivotViewer dimension grouping contracts and localize toolbar copy

[woksin]

At commit ba9155d, PivotViewer has observable grouping and copy mismatches. Source/PivotViewer/types.ts:66-77 exposes PivotDimension.formatValue and sort, but the rendered grouping path calls the engine with only currentGroupBy (Source/PivotViewer/PivotViewer.tsx:243-245); Source/PivotViewer/engine/store.ts:300-335 emits raw labels and default sorting without those callbacks. Its computeGrouping only handles strings and numbers (engine/store.ts:300-312), and buildIndexes ignores boolean fields (engine/store.ts:145-161), so a boolean dimension produces no groups. buildStore picks the field kind from the first item (engine/store.ts:31-55), so an initial null or undefined can turn a numeric field into strings. Source/PivotViewer/components/Toolbar.tsx:42,94-102,107-147 hardcodes "Sort by", "events", and zoom/filter labels in English; "events" also mislabels non-event collections.

Custom dimension display/order is ignored, some valid data cannot be grouped correctly, and the viewer cannot fully reflect the host language or domain.

Done when

• Rendered groups honor the declared dimension formatter and comparator, including the worker and fallback paths.
• Boolean dimensions form groups and sparse first rows do not change the field type incorrectly.
• Toolbar count and controls use overridable/localizable labels rather than event-specific hardcoding, with focused coverage.

[github-actions]

Closed by release v4.15.1.

[woksin]

Reopened: 4.15.1 (#345) delivered the grouping part. Boolean columns now group and filter, missing values stay missing, columns infer their type from the first non-missing value, and the declared formatValue and sort are applied. Still open: localizable PivotViewer toolbar text and item count, which adds public props and is in progress for 4.16.0.