- Extract shared defaultReferencePeriod helper (src/utils/referencePeriod.ts)
- useHighlights now reads ?refY=YYYY&refM=MM, defaults to previous month
- getHighlights signature: (referenceYear, referenceMonth, ytdYear, windowDays, ...)
- YTD tile pinned to Jan 1 of current civil year, independent of reference month
- CompareReferenceMonthPicker surfaced on /reports/highlights
- Hub highlights panel inherits the same default via useHighlights
- useCartes and useCompare now delegate their default-period helpers to the shared util