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/main.dart

@@ -11,6 +11,7 @@ import 'package:em2rp/views/equipment_management_page.dart';
 import 'package:em2rp/views/container_management_page.dart';
 import 'package:em2rp/views/container_form_page.dart';
 import 'package:em2rp/views/container_detail_page.dart';
+import 'package:em2rp/views/event_preparation_page.dart';
 import 'package:em2rp/models/container_model.dart';
 import 'package:firebase_auth/firebase_auth.dart';
 import 'package:flutter/material.dart';
@@ -150,6 +151,12 @@ class MyApp extends StatelessWidget {
             child: ContainerDetailPage(container: container),
           );
         },
+        '/event_preparation': (context) {
+          final eventId = ModalRoute.of(context)!.settings.arguments as String;
+          return AuthGuard(
+            child: EventPreparationPage(eventId: eventId),
+          );
+        },
       },
     );
   }