feat(shared): legacy presentation/ + shared design system + widgets

- lib/presentation : pages legacy (explore/network, notifications) avec BLoC
- lib/shared/design_system : UnionFlow Design System v2 (tokens, components)
  + MD3 tokens + module_colors par feature
- lib/shared/widgets : widgets transversaux (core_card, core_shimmer,
  error_widget, loading_widget, powered_by_lions_dev, etc.)
- lib/shared/constants + utils

lib/shared/widgets/validated_text_field.dart

@@ -3,6 +3,7 @@ library validated_text_field;
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
+import '../design_system/tokens/app_colors.dart';
 
 /// Validated text field with consistent styling and behavior
 class ValidatedTextField extends StatelessWidget {
@@ -61,6 +62,7 @@ class ValidatedTextField extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final isDark = Theme.of(context).brightness == Brightness.dark;
     return TextFormField(
       controller: controller,
       initialValue: initialValue,
@@ -73,30 +75,32 @@ class ValidatedTextField extends StatelessWidget {
         border: const OutlineInputBorder(),
         enabledBorder: OutlineInputBorder(
           borderSide: BorderSide(
-            color: Colors.grey.shade400,
+            color: isDark ? AppColors.borderDark : AppColors.border,
             width: 1.0,
           ),
         ),
-        focusedBorder: const OutlineInputBorder(
+        focusedBorder: OutlineInputBorder(
           borderSide: BorderSide(
-            color: Colors.blue,
+            color: AppColors.primary,
             width: 2.0,
           ),
         ),
-        errorBorder: const OutlineInputBorder(
+        errorBorder: OutlineInputBorder(
           borderSide: BorderSide(
-            color: Colors.red,
+            color: AppColors.error,
             width: 1.0,
           ),
         ),
-        focusedErrorBorder: const OutlineInputBorder(
+        focusedErrorBorder: OutlineInputBorder(
           borderSide: BorderSide(
-            color: Colors.red,
+            color: AppColors.error,
             width: 2.0,
           ),
         ),
         filled: !enabled,
-        fillColor: !enabled ? Colors.grey.shade100 : null,
+        fillColor: !enabled
+            ? (isDark ? AppColors.surfaceVariantDark : AppColors.backgroundSubtle)
+            : null,
         counterText: showCounter ? null : '',
       ),
       validator: validator,
@@ -165,10 +169,10 @@ class ValidatedAmountField extends StatelessWidget {
         padding: const EdgeInsets.all(12.0),
         child: Text(
           currencySymbol,
-          style: const TextStyle(
+          style: TextStyle(
             fontSize: 16,
             fontWeight: FontWeight.bold,
-            color: Colors.grey,
+            color: AppColors.textTertiary,
           ),
         ),
       ),
@@ -206,6 +210,7 @@ class ValidatedDropdownField<T> extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final isDark = Theme.of(context).brightness == Brightness.dark;
     return DropdownButtonFormField<T>(
       value: value,
       items: items,
@@ -216,24 +221,26 @@ class ValidatedDropdownField<T> extends StatelessWidget {
         border: const OutlineInputBorder(),
         enabledBorder: OutlineInputBorder(
           borderSide: BorderSide(
-            color: Colors.grey.shade400,
+            color: isDark ? AppColors.borderDark : AppColors.border,
             width: 1.0,
           ),
         ),
-        focusedBorder: const OutlineInputBorder(
+        focusedBorder: OutlineInputBorder(
           borderSide: BorderSide(
-            color: Colors.blue,
+            color: AppColors.primary,
             width: 2.0,
           ),
         ),
-        errorBorder: const OutlineInputBorder(
+        errorBorder: OutlineInputBorder(
           borderSide: BorderSide(
-            color: Colors.red,
+            color: AppColors.error,
             width: 1.0,
           ),
         ),
         filled: !enabled,
-        fillColor: !enabled ? Colors.grey.shade100 : null,
+        fillColor: !enabled
+            ? (isDark ? AppColors.surfaceVariantDark : AppColors.backgroundSubtle)
+            : null,
       ),
       validator: validator,
       onChanged: enabled ? onChanged : null,
@@ -269,6 +276,7 @@ class ValidatedDateField extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final isDark = Theme.of(context).brightness == Brightness.dark;
     return InkWell(
       onTap: enabled
           ? () async {
@@ -292,24 +300,26 @@ class ValidatedDateField extends StatelessWidget {
           border: const OutlineInputBorder(),
           enabledBorder: OutlineInputBorder(
             borderSide: BorderSide(
-              color: Colors.grey.shade400,
+              color: isDark ? AppColors.borderDark : AppColors.border,
               width: 1.0,
             ),
           ),
-          focusedBorder: const OutlineInputBorder(
+          focusedBorder: OutlineInputBorder(
             borderSide: BorderSide(
-              color: Colors.blue,
+              color: AppColors.primary,
               width: 2.0,
             ),
           ),
-          errorBorder: const OutlineInputBorder(
+          errorBorder: OutlineInputBorder(
             borderSide: BorderSide(
-              color: Colors.red,
+              color: AppColors.error,
               width: 1.0,
             ),
           ),
           filled: !enabled,
-          fillColor: !enabled ? Colors.grey.shade100 : null,
+          fillColor: !enabled
+              ? (isDark ? AppColors.surfaceVariantDark : AppColors.backgroundSubtle)
+              : null,
           errorText: validator != null ? validator!(selectedDate) : null,
         ),
         child: Text(
@@ -317,7 +327,9 @@ class ValidatedDateField extends StatelessWidget {
               ? '${selectedDate!.day}/${selectedDate!.month}/${selectedDate!.year}'
               : hintText ?? 'Sélectionner une date',
           style: TextStyle(
-            color: selectedDate != null ? Colors.black87 : Colors.grey,
+            color: selectedDate != null
+                ? (isDark ? AppColors.textPrimaryDark : AppColors.textPrimary)
+                : AppColors.textTertiary,
           ),
         ),
       ),