feat(leave) : align forfait CP N + display remaining workdays + N-1 absences exempt from presence

- LeaveRecapRowBuilder: forfait CP N now reflects remainingDays (acquis − pris depuis N) instead of the constant acquiredDays. Affects both PDF export and screen recap.
- Employee detail header: forfait label becomes "Forfait - 218 jours (X restants)" where X = 218 − presence days from Jan 1 to today (today included).
- New EmployeeLeaveSummary.presenceDaysToToday field, computed via the same logic as presenceDaysByMonth but capped at today.
- Forfait business rule: leaves attributed to N-1 stock no longer decrement presence days. Implemented by chronologically consuming an N-1 budget (= previousYearTakenDays) inside computePresenceDaysByMonth before counting any absence. Non-forfait unaffected (budget is 0).
- Doc updates: CLAUDE.md (forfait/N-1 rule), functional-rules.md (CP N forfait semantics).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

doc/functional-rules.md

@@ -335,7 +335,7 @@ Tous les filtres checkbox sont cochés par défaut à l'ouverture du drawer.
 | Contrat | Contract.name |
 | CP N-1 restant | CDI/CDD: acquis N-1 − pris sur N-1. Forfait: report N-1 restant |
 | Samedi restant | CDI/CDD: samedis acquis N-1 − pris. Forfait: `-` |
-| CP N | Forfait: jours acquis année civile. Non-forfait: en cours d'acquisition |
+| CP N | Forfait: restant sur quota année civile (acquis − pris depuis N, sans toucher au stock N-1). Non-forfait: en cours d'acquisition |
 | RTT | Minutes disponibles (report N-1 + acquis N - payés). Format `X h Y m`. Forfait et INTERIM: `-` |
 
 ## 10bis) Écran Récap. congés (tableau)