feat: Add full-screen receipt viewer, display trip participants in calendar, and restrict trip management options to creator.

lib/components/home/calendar/calendar_page.dart_snippet

@@ -0,0 +1,59 @@
+  void _showParticipantsDialog(BuildContext context) {
+    showDialog(
+      context: context,
+      builder: (context) => AlertDialog(
+        title: const Text('Participants'),
+        content: SizedBox(
+          width: double.maxFinite,
+          child: FutureBuilder<List<User>>(
+            future: UserRepository().getUsersByIds([
+              ...widget.trip.participants,
+              widget.trip.createdBy,
+            ]),
+            builder: (context, snapshot) {
+              if (snapshot.connectionState == ConnectionState.waiting) {
+                return const Center(child: CircularProgressIndicator());
+              }
+              
+              if (snapshot.hasError) {
+                return const Center(child: Text('Erreur de chargement'));
+              }
+
+              final users = snapshot.data ?? [];
+              if (users.isEmpty) {
+                return const Center(child: Text('Aucun participant trouvé'));
+              }
+
+              return ListView.builder(
+                shrinkWrap: true,
+                itemCount: users.length,
+                itemBuilder: (context, index) {
+                  final user = users[index];
+                  final isCreator = user.id == widget.trip.createdBy;
+                  
+                  return ListTile(
+                    leading: CircleAvatar(
+                      backgroundImage: user.photoUrl != null
+                          ? NetworkImage(user.photoUrl!)
+                          : null,
+                      child: user.photoUrl == null
+                          ? Text(user.initials)
+                          : null,
+                    ),
+                    title: Text(user.fullName),
+                    subtitle: isCreator ? const Text('Organisateur') : null,
+                  );
+                },
+              );
+            },
+          ),
+        ),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context),
+            child: const Text('Fermer'),
+          ),
+        ],
+      ),
+    );
+  }