feat(inscription): payload enfant/photo et limite JSON 15 Mo côté API

- Express/Nest : body parser json et urlencoded à 15 Mo pour les photos base64.
- Front : envoi d’inscription parent (authService, payload, étape 3).

Made-with: Cursor

frontend/lib/utils/parent_registration_payload.dart

@@ -102,7 +102,7 @@ class ParentRegistrationPayload {
     final tel = _normalizePhone(p1.phone);
 
     final body = <String, dynamic>{
-      'email': p1.email.trim(),
+      'email': normalizeEmailText(p1.email),
       'prenom': p1.firstName.trim(),
       'nom': p1.lastName.trim(),
       'telephone': tel,
@@ -188,6 +188,51 @@ class ParentRegistrationPayload {
     return map;
   }
 
+  /// Sous-type `image/…` pour data-URL et extension côté API (`jpeg`, `png`, `gif`, `heic`, …).
+  static String _imageMimeFromMagicBytes(Uint8List bytes) {
+    if (bytes.length >= 8) {
+      if (bytes[0] == 0x89 &&
+          bytes[1] == 0x50 &&
+          bytes[2] == 0x4E &&
+          bytes[3] == 0x47) {
+        return 'png';
+      }
+      if (bytes[0] == 0xFF && bytes[1] == 0xD8) {
+        return 'jpeg';
+      }
+      if (bytes.length >= 12 &&
+          bytes[0] == 0x52 &&
+          bytes[1] == 0x49 &&
+          bytes[2] == 0x46 &&
+          bytes[3] == 0x46) {
+        return 'webp';
+      }
+      if (bytes.length >= 6 &&
+          bytes[0] == 0x47 &&
+          bytes[1] == 0x49 &&
+          bytes[2] == 0x46 &&
+          bytes[3] == 0x38 &&
+          (bytes[4] == 0x37 || bytes[4] == 0x39) &&
+          bytes[5] == 0x61) {
+        return 'gif';
+      }
+      if (bytes.length >= 12 &&
+          bytes[4] == 0x66 &&
+          bytes[5] == 0x74 &&
+          bytes[6] == 0x79 &&
+          bytes[7] == 0x70) {
+        final a = bytes[8], b = bytes[9], c = bytes[10], d = bytes[11];
+        if ((a == 0x68 && b == 0x65 && c == 0x69 && d == 0x63) ||
+            (a == 0x68 && b == 0x65 && c == 0x69 && d == 0x78) ||
+            (a == 0x6d && b == 0x69 && c == 0x66 && d == 0x31) ||
+            (a == 0x6d && b == 0x73 && c == 0x66 && d == 0x31)) {
+          return 'heic';
+        }
+      }
+    }
+    return 'jpeg';
+  }
+
   /// (`dataUrl`, `filename`) ou `null` si pas de fichier lisible.
   static (String, String)? _childPhotoBase64(ChildData c, int index, String prenom) {
     Uint8List? bytes = c.imageBytes;
@@ -203,23 +248,7 @@ class ParentRegistrationPayload {
     }
     if (bytes.isEmpty) return null;
     final b64 = base64Encode(bytes);
-    var mime = 'jpeg';
-    if (bytes.length >= 8) {
-      if (bytes[0] == 0x89 &&
-          bytes[1] == 0x50 &&
-          bytes[2] == 0x4E &&
-          bytes[3] == 0x47) {
-        mime = 'png';
-      } else if (bytes[0] == 0xFF && bytes[1] == 0xD8) {
-        mime = 'jpeg';
-      } else if (bytes.length >= 12 &&
-          bytes[0] == 0x52 &&
-          bytes[1] == 0x49 &&
-          bytes[2] == 0x46 &&
-          bytes[3] == 0x46) {
-        mime = 'webp';
-      }
-    }
+    final mime = _imageMimeFromMagicBytes(bytes);
     final safeName = prenom.isNotEmpty
         ? '${prenom.toLowerCase().replaceAll(RegExp(r'[^a-z0-9]+'), '_')}.$mime'
         : 'enfant_${index + 1}.$mime';