feat: Refactor event equipment management with advanced selection and conflict detection

This commit introduces a complete overhaul of how equipment is assigned to events, focusing on an enhanced user experience, advanced selection capabilities, and robust conflict detection.

**Key Features & Enhancements:**

-   **Advanced Equipment Selection UI (`EquipmentSelectionDialog`):**
    -   New full-screen dialog to select equipment and containers ("boîtes") for an event.
    -   Hierarchical view showing containers and a flat list of all individual equipment.
    -   Real-time search and filtering by equipment category.
    -   Side panel summarizing the current selection and providing recommendations for containers based on selected equipment.
    -   Supports quantity selection for consumables and cables.

-   **Conflict Detection & Management (`EventAvailabilityService`):**
    -   A new service (`EventAvailabilityService`) checks for equipment availability against other events based on the selected date range.
    -   The selection dialog visually highlights equipment and containers with scheduling conflicts (e.g., already used, partially unavailable).
    -   A dedicated conflict resolution dialog (`EquipmentConflictDialog`) appears if conflicting items are selected, allowing the user to either remove them or force the assignment.

-   **Integrated Event Form (`EventAssignedEquipmentSection`):**
    -   The event creation/editing form now includes a new section for managing assigned equipment.
    -   It clearly displays assigned containers and standalone equipment, showing the composition of each container.
    -   Integrates the new selection dialog, ensuring all assignments are checked for conflicts before being saved.

-   **Event Preparation & Return Workflow (`EventPreparationPage`):**
    -   New page (`EventPreparationPage`) for managing the check-out (preparation) and check-in (return) of equipment for an event.
    -   Provides a checklist of all assigned equipment.
    -   Users can validate each item, with options to "validate all" or finalize with missing items.
    -   Includes a dialog (`MissingEquipmentDialog`) to handle discrepancies.
    -   Supports tracking returned quantities for consumables.

**Data Model and Other Changes:**

-   The `EventModel` now includes `assignedContainers` to explicitly link containers to an event.
-   `EquipmentAssociatedEventsSection` on the equipment detail page is now functional, displaying current, upcoming, and past events for that item.
-   Added deployment and versioning scripts (`scripts/deploy.js`, `scripts/increment_version.js`, `scripts/toggle_env.js`) to automate the release process.
-   Introduced an application version display in the main drawer (`AppVersion`).

em2rp/lib/services/event_preparation_service.dart

@@ -148,7 +148,10 @@ class EventPreparationService {
   }
 
   /// Valider tous les retours
-  Future<void> validateAllReturn(String eventId) async {
+  Future<void> validateAllReturn(
+    String eventId, [
+    Map<String, int>? returnedQuantities,
+  ]) async {
     try {
       final event = await _getEvent(eventId);
       if (event == null) {
@@ -157,9 +160,12 @@ class EventPreparationService {
 
       // Marquer tous les équipements comme retournés
       final updatedEquipment = event.assignedEquipment.map((eq) {
+        final returnedQty = returnedQuantities?[eq.equipmentId] ??
+                           eq.returnedQuantity ??
+                           eq.quantity;
         return eq.copyWith(
           isReturned: true,
-          returnedQuantity: eq.returnedQuantity ?? eq.quantity,
+          returnedQuantity: returnedQty,
         );
       }).toList();