fix(session): keep weapon selection valid when returning from the armory

lib/features/session/session_setup_screen.dart

@@ -27,6 +27,12 @@ class _SessionSetupScreenState extends State<SessionSetupScreen> {
 
   DateTime _selectedDate = DateTime.now();
 
+  /// Valeur sentinelle de l'item "Ajouter une nouvelle arme" du menu deroulant.
+  static const String _addWeaponValue = '__add_weapon__';
+
+  final GlobalKey<FormFieldState<String>> _weaponFieldKey =
+      GlobalKey<FormFieldState<String>>();
+
   static const List<int> _presetDistances = [10, 15, 25, 50, 100, 200];
   static const List<int> _presetShots = [3, 5, 10, 15, 20, 30, 50];
 
@@ -44,8 +50,21 @@ class _SessionSetupScreenState extends State<SessionSetupScreen> {
     if (mounted) {
       setState(() {
         _availableWeapons = weapons;
-        if (_availableWeapons.isNotEmpty && _selectedWeapon == null) {
-          _selectedWeapon = _availableWeapons.first;
+
+        // Les armes rechargees sont de nouvelles instances (Weapon n'a pas
+        // d'operator ==) et l'arme selectionnee a pu etre supprimee : on
+        // re-resout la selection par identifiant.
+        final previousId = _selectedWeapon?.id;
+        _selectedWeapon = null;
+        for (final weapon in weapons) {
+          if (weapon.id == previousId) {
+            _selectedWeapon = weapon;
+            break;
+          }
+        }
+
+        if (_selectedWeapon == null && weapons.isNotEmpty) {
+          _selectedWeapon = weapons.first;
           _updateSettingsForWeapon(_selectedWeapon!);
         }
         _isLoadingWeapons = false;
@@ -237,44 +256,64 @@ class _SessionSetupScreenState extends State<SessionSetupScreen> {
               ],
             ),
             const SizedBox(height: 16),
-            DropdownButtonFormField<Weapon>(
-              initialValue: _selectedWeapon,
+            DropdownButtonFormField<String>(
+              key: _weaponFieldKey,
+              initialValue: _selectedWeapon?.id,
               decoration: const InputDecoration(
                 labelText: 'Arme utilisée',
                 prefixIcon: Icon(Icons.shield_outlined),
               ),
-              items: _availableWeapons
-                  .map(
-                    (w) => DropdownMenuItem(
-                      value: w,
-                      child: Text('${w.displayName} (${w.caliber})'),
-                    ),
-                  )
-                  .toList(),
+              items: [
+                ..._availableWeapons.map(
+                  (w) => DropdownMenuItem(
+                    value: w.id,
+                    child: Text('${w.displayName} (${w.caliber})'),
+                  ),
+                ),
+                DropdownMenuItem(
+                  value: _addWeaponValue,
+                  child: Row(
+                    children: [
+                      Icon(
+                        Icons.add_circle_outline,
+                        size: 18,
+                        color: Theme.of(context).colorScheme.primary,
+                      ),
+                      const SizedBox(width: 8),
+                      Text(
+                        'Ajouter une nouvelle arme',
+                        style: TextStyle(
+                          fontWeight: FontWeight.w600,
+                          color: Theme.of(context).colorScheme.primary,
+                        ),
+                      ),
+                    ],
+                  ),
+                ),
+              ],
               onChanged: (value) {
-                if (value != null) {
-                  setState(() {
-                    _selectedWeapon = value;
-                    _updateSettingsForWeapon(value);
-                  });
+                if (value == null) return;
+
+                if (value == _addWeaponValue) {
+                  // L'item d'action n'est pas une arme : on restaure aussitot
+                  // la selection precedente avant d'ouvrir l'armurerie.
+                  _weaponFieldKey.currentState?.didChange(_selectedWeapon?.id);
+                  _openArmory();
+                  return;
+                }
+
+                for (final weapon in _availableWeapons) {
+                  if (weapon.id == value) {
+                    setState(() {
+                      _selectedWeapon = weapon;
+                      _updateSettingsForWeapon(weapon);
+                    });
+                    break;
+                  }
                 }
               },
             ),
-            const SizedBox(height: 4),
-            Align(
-              alignment: Alignment.centerLeft,
-              child: TextButton.icon(
-                onPressed: _openArmory,
-                icon: const Icon(Icons.add_circle_outline, size: 18),
-                label: const Text('Ajouter une nouvelle arme'),
-                style: TextButton.styleFrom(
-                  padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 4),
-                  visualDensity: VisualDensity.compact,
-                  tapTargetSize: MaterialTapTargetSize.shrinkWrap,
-                ),
-              ),
-            ),
-            const SizedBox(height: 8),
+            const SizedBox(height: 12),
             InkWell(
               onTap: _pickDate,
               borderRadius: BorderRadius.circular(12),