feat: inventaire bovins (!49)

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

## Description de la PR

## Modification du .env

## Check list

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

Reviewed-on: #49
Co-authored-by: tristan <tristan@yuno.malio.fr>
Co-committed-by: tristan <tristan@yuno.malio.fr>

frontend/utils/bovine-age.ts

@@ -0,0 +1,10 @@
+export const formatAgeLabel = (months: number | null | undefined): string => {
+    if (months === null || months === undefined) return '—'
+    const years = Math.floor(months / 12)
+    const remaining = months % 12
+    let label = ''
+    if (years > 0) label = `${years} an${years > 1 ? 's' : ''}`
+    if (remaining > 0) label += `${label ? ' ' : ''}${remaining} mois`
+    if (!label) label = '< 1 mois'
+    return label
+}