[#MUI-33] Développer le composant Datepicker (#50)

| Numéro du ticket | Titre du ticket |
|------------------|-----------------|
|                  |                 |

## Description de la PR

## Modification du .env

## Check list

- [x] Pas de régression
- [x] TU/TI/TF rédigée
- [x] TU/TI/TF OK
- [x] CHANGELOG modifié

Reviewed-on: #50
Co-authored-by: tristan <tristan@yuno.malio.fr>
Co-committed-by: tristan <tristan@yuno.malio.fr>

app/components/malio/date/composables/dateRange.ts

@@ -0,0 +1,31 @@
+export type DateRangeValue = {start: string; end: string}
+
+export function normalizeRange(a: string, b: string): DateRangeValue {
+  return a <= b ? {start: a, end: b} : {start: b, end: a}
+}
+
+export function resolveRangeBounds(
+  start: string | null,
+  end: string | null,
+  preview: string | null,
+): {lo: string; hi: string} | null {
+  if (!start) return null
+  const other = end ?? preview
+  if (!other) return {lo: start, hi: start}
+  return start <= other ? {lo: start, hi: other} : {lo: other, hi: start}
+}
+
+export type DayRangeRole = 'none' | 'single' | 'start' | 'end' | 'in-range'
+
+export function dayRangeRole(
+  iso: string,
+  bounds: {lo: string; hi: string} | null,
+): DayRangeRole {
+  if (!bounds) return 'none'
+  const {lo, hi} = bounds
+  if (lo === hi) return iso === lo ? 'single' : 'none'
+  if (iso === lo) return 'start'
+  if (iso === hi) return 'end'
+  if (iso > lo && iso < hi) return 'in-range'
+  return 'none'
+}