feat(frontend): Refonte infrastructure formulaires multi-modes

- Support des modes Desktop/Mobile et Édition/Lecture seule
- Refactoring des widgets de formulaire (PersonalInfo, ProfessionalInfo, Presentation, ChildCard)
- Mise à jour des écrans de récapitulatif (ParentStep5, AmStep4)
- Ajout de navigation (Précédent/Soumettre) sur mobile

Closes #78

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

frontend/lib/widgets/summary_screen.dart

@@ -38,7 +38,7 @@ class SummaryScreen extends StatelessWidget {
           actions: [
             Center(
               child: ImageButton(
-                bg: 'assets/images/btn_green.png',
+                bg: 'assets/images/bg_green.png',
                 text: 'OK',
                 textColor: const Color(0xFF2D6A4F),
                 width: 150,
@@ -89,7 +89,7 @@ class SummaryScreen extends StatelessWidget {
                     const SizedBox(height: 20),
                     
                     ImageButton(
-                      bg: 'assets/images/btn_green.png',
+                      bg: 'assets/images/bg_green.png',
                       text: submitButtonText,
                       textColor: const Color(0xFF2D6A4F),
                       width: 350,
@@ -230,11 +230,12 @@ Widget buildDisplayFieldValue(
         height: multiLine ? null : fieldHeight,
         constraints: multiLine ? const BoxConstraints(minHeight: 50.0) : null,
         padding: const EdgeInsets.symmetric(horizontal: 18.0, vertical: 12.0),
-        decoration: const BoxDecoration(
-          image: DecorationImage(
-            image: AssetImage('assets/images/input_field_bg.png'),
+        decoration: BoxDecoration(
+          image: const DecorationImage(
+            image: AssetImage('assets/images/bg_beige.png'),
             fit: BoxFit.fill,
           ),
+          borderRadius: BorderRadius.circular(8),
         ),
         child: Text(
           value.isNotEmpty ? value : '-',