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

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## 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/dateWeek.test.ts

@@ -0,0 +1,74 @@
+import {describe, expect, it} from 'vitest'
+import {
+  formatWeekDisplay,
+  isValidIsoWeek,
+  isoWeekToMonday,
+  mondayOf,
+  sundayOf,
+  toIsoWeek,
+} from './dateWeek'
+
+describe('dateWeek', () => {
+  describe('mondayOf / sundayOf', () => {
+    it('returns Monday and Sunday of a midweek date', () => {
+      expect(mondayOf('2026-05-20')).toBe('2026-05-18') // mercredi
+      expect(sundayOf('2026-05-20')).toBe('2026-05-24')
+    })
+    it('keeps Monday on a Monday', () => {
+      expect(mondayOf('2026-05-18')).toBe('2026-05-18')
+    })
+    it('returns the preceding Monday for a Sunday', () => {
+      expect(mondayOf('2026-05-24')).toBe('2026-05-18')
+    })
+  })
+
+  describe('toIsoWeek', () => {
+    it('returns the ISO week of a date', () => {
+      expect(toIsoWeek('2026-05-20')).toBe('2026-W21')
+    })
+    it('handles year boundaries', () => {
+      expect(toIsoWeek('2026-01-01')).toBe('2026-W01')
+      expect(toIsoWeek('2025-12-31')).toBe('2026-W01')
+      expect(toIsoWeek('2027-01-01')).toBe('2026-W53')
+    })
+  })
+
+  describe('isoWeekToMonday', () => {
+    it('returns the Monday of a week string', () => {
+      expect(isoWeekToMonday('2026-W21')).toBe('2026-05-18')
+    })
+    it('round-trips with toIsoWeek', () => {
+      for (const w of ['2026-W01', '2026-W21', '2026-W53', '2024-W09']) {
+        const monday = isoWeekToMonday(w)
+        expect(monday).not.toBeNull()
+        expect(toIsoWeek(monday as string)).toBe(w)
+      }
+    })
+    it('returns null for invalid input', () => {
+      expect(isoWeekToMonday('2026-21')).toBeNull()
+      expect(isoWeekToMonday('2026-W00')).toBeNull()
+      expect(isoWeekToMonday('2026-W54')).toBeNull()
+      expect(isoWeekToMonday('2025-W53')).toBeNull() // 2025 n'a que 52 semaines ISO
+    })
+  })
+
+  describe('isValidIsoWeek', () => {
+    it('accepts a real ISO week', () => {
+      expect(isValidIsoWeek('2026-W21')).toBe(true)
+    })
+    it('rejects malformed or impossible weeks', () => {
+      expect(isValidIsoWeek('2026-21')).toBe(false)
+      expect(isValidIsoWeek('2026-W00')).toBe(false)
+      expect(isValidIsoWeek('2026-W54')).toBe(false)
+    })
+  })
+
+  describe('formatWeekDisplay', () => {
+    it('formats a week as a human label', () => {
+      expect(formatWeekDisplay('2026-W21')).toBe('Semaine 21 (18/05 → 24/05/2026)')
+    })
+    it('returns empty string for invalid input', () => {
+      expect(formatWeekDisplay('2026-W54')).toBe('')
+    })
+  })
+})