fix(#112): dates et places AM en reprise (resetForReprise)

Corrige l’ombre des paramètres dateOfBirth, agreementDate et placesAvailable
dans resetForReprise ; renforce le parsing reprise-dossier et ajoute un test.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/lib/utils/reprise_mapper.dart

@@ -108,6 +108,15 @@ class RepriseMapper {
   static DateTime? parseIsoDate(String? raw) {
     if (raw == null || raw.trim().isEmpty) return null;
     final s = raw.trim();
+    final iso = RegExp(r'^(\d{4})-(\d{2})-(\d{2})');
+    final isoMatch = iso.firstMatch(s);
+    if (isoMatch != null) {
+      return DateTime(
+        int.parse(isoMatch.group(1)!),
+        int.parse(isoMatch.group(2)!),
+        int.parse(isoMatch.group(3)!),
+      );
+    }
     try {
       return DateTime.parse(s);
     } catch (_) {
@@ -128,10 +137,34 @@ class RepriseMapper {
     if (value == null) return null;
     if (value is String) {
       final s = value.trim();
-      return s.isEmpty ? null : s;
+      return s.isEmpty || s == 'null' ? null : s;
     }
-    if (value is DateTime) return value.toIso8601String();
-    return null;
+    if (value is DateTime) {
+      return '${value.year.toString().padLeft(4, '0')}-'
+          '${value.month.toString().padLeft(2, '0')}-'
+          '${value.day.toString().padLeft(2, '0')}';
+    }
+    if (value is num) {
+      final ms = value.abs() > 9999999999
+          ? value.toInt()
+          : value.toInt() * 1000;
+      final dt = DateTime.fromMillisecondsSinceEpoch(ms, isUtc: true);
+      return '${dt.year.toString().padLeft(4, '0')}-'
+          '${dt.month.toString().padLeft(2, '0')}-'
+          '${dt.day.toString().padLeft(2, '0')}';
+    }
+    if (value is Map) {
+      final y = value['year'];
+      final m = value['month'] ?? value['monthValue'];
+      final d = value['day'] ?? value['dayOfMonth'];
+      if (y is num && m is num && d is num) {
+        return '${y.toInt().toString().padLeft(4, '0')}-'
+            '${m.toInt().toString().padLeft(2, '0')}-'
+            '${d.toInt().toString().padLeft(2, '0')}';
+      }
+    }
+    final s = value.toString().trim();
+    return s.isEmpty || s == 'null' ? null : s;
   }
 
   static int? optionalInt(dynamic value) {