feat(features): refontes onboarding/organizations/profile/reports/settings/solidarity

- onboarding : datasource souscription, models formule/status, bloc complet
- organizations : bloc orgs + switcher + types bloc, models, pages edit/create
- profile : bloc complet avec change password, delete account, preferences
- reports : bloc avec DashboardReports + ScheduleReports + GenerateReport
- settings : language, privacy, feedback pages
- solidarity : bloc complet demandes d'aide (CRUD, approuver, rejeter)

lib/features/onboarding/presentation/pages/period_selection_page.dart

@@ -63,7 +63,7 @@ class _PeriodSelectionPageState extends State<PeriodSelectionPage> {
     final prixSelected = _estimerPrix(_selectedPeriode);
 
     return Scaffold(
-      backgroundColor: UnionFlowColors.background,
+      backgroundColor: Theme.of(context).scaffoldBackgroundColor,
       body: Column(
         children: [
           OnboardingStepHeader(