feat: Add calendar page, enhance activity search and approval logic, and refactor activity filtering UI.

lib/models/activity.dart

@@ -20,6 +20,7 @@ class Activity {
   final Map<String, int> votes; // userId -> vote (1 pour pour, -1 pour contre)
   final DateTime createdAt;
   final DateTime updatedAt;
+  final DateTime? date; // Date prévue pour l'activité
 
   Activity({
     required this.id,
@@ -40,6 +41,7 @@ class Activity {
     this.votes = const {},
     required this.createdAt,
     required this.updatedAt,
+    this.date,
   });
 
   /// Calcule le score total des votes
@@ -104,6 +106,8 @@ class Activity {
     Map<String, int>? votes,
     DateTime? createdAt,
     DateTime? updatedAt,
+    DateTime? date,
+    bool clearDate = false,
   }) {
     return Activity(
       id: id ?? this.id,
@@ -124,6 +128,7 @@ class Activity {
       votes: votes ?? this.votes,
       createdAt: createdAt ?? this.createdAt,
       updatedAt: updatedAt ?? this.updatedAt,
+      date: clearDate ? null : (date ?? this.date),
     );
   }
 
@@ -148,6 +153,7 @@ class Activity {
       'votes': votes,
       'createdAt': Timestamp.fromDate(createdAt),
       'updatedAt': Timestamp.fromDate(updatedAt),
+      'date': date != null ? Timestamp.fromDate(date!) : null,
     };
   }
 
@@ -172,6 +178,7 @@ class Activity {
       votes: Map<String, int>.from(map['votes'] ?? {}),
       createdAt: (map['createdAt'] as Timestamp).toDate(),
       updatedAt: (map['updatedAt'] as Timestamp).toDate(),
+      date: map['date'] != null ? (map['date'] as Timestamp).toDate() : null,
     );
   }