[#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/dateFormat.ts

@@ -0,0 +1,26 @@
+export function isValidIso(iso: string): boolean {
+  if (!/^\d{4}-\d{2}-\d{2}$/.test(iso)) return false
+  const [y, m, d] = iso.split('-').map(Number)
+  const date = new Date(y, m - 1, d)
+  return date.getFullYear() === y && date.getMonth() === m - 1 && date.getDate() === d
+}
+
+export function formatIsoToDisplay(iso: string | null): string {
+  if (!iso || !isValidIso(iso)) return ''
+  const [y, m, d] = iso.split('-')
+  return `${d}/${m}/${y}`
+}
+
+export function parseDisplayToIso(display: string): string | null {
+  const match = /^(\d{2})\/(\d{2})\/(\d{4})$/.exec(display.trim())
+  if (!match) return null
+  const [, dd, mm, yyyy] = match
+  const iso = `${yyyy}-${mm}-${dd}`
+  return isValidIso(iso) ? iso : null
+}
+
+export function isDateInRange(iso: string, min?: string, max?: string): boolean {
+  if (min && iso < min) return false
+  if (max && iso > max) return false
+  return true
+}