feat(heures) : affichage des jours travaillés (CUSTOM) sur la vue Jour

Le libellé sous le nom de l'employé affiche en suffixe les jours du planning
workDaysHours au format court (ex. BUREAU — CDI — LU,JE) pour les contrats CUSTOM.
Résolu à la date filtrée et exposé via WorkHourDayContext.workDaysHours ; formaté
front par formatWorkedDaysShort. Limité aux CUSTOM (35h/39h/forfait/intérim sans
planning → rien affiché) et à l'écran Heures (pas Heures Conducteurs).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/utils/contract.ts

@@ -37,6 +37,26 @@ export const requiresWorkDaysHours = (
 
 const DAY_SHORT_LABELS: Record<number, string> = { 1: 'Lun', 2: 'Mar', 3: 'Mer', 4: 'Jeu', 5: 'Ven' }
 
+const DAY_TINY_LABELS: Record<number, string> = { 1: 'LU', 2: 'MA', 3: 'ME', 4: 'JE', 5: 'VE' }
+
+/**
+ * Very compact worked-days summary for the day view header, e.g. "LU,VE".
+ * Lists the iso days actually worked (minutes > 0), uppercase 2-letter, comma-separated.
+ * Returns null when the schedule is empty/unset (non-CUSTOM contracts have no schedule).
+ */
+export const formatWorkedDaysShort = (
+  workDaysHours: Record<number, number> | null | undefined
+): string | null => {
+  if (!workDaysHours) return null
+  const days = Object.entries(workDaysHours)
+    .map(([iso, minutes]) => [Number(iso), Number(minutes)] as const)
+    .filter(([iso, minutes]) => iso >= 1 && iso <= 5 && minutes > 0)
+    .sort(([a], [b]) => a - b)
+    .map(([iso]) => DAY_TINY_LABELS[iso])
+  if (days.length === 0) return null
+  return days.join(',')
+}
+
 /**
  * Compact human-readable summary of a per-day schedule, e.g. "Lun 2h, Jeu 2h".
  * Returns null when the schedule is empty/unset.