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

lib/components/account/expense_detail_dialog.dart

@@ -322,7 +322,40 @@ class ExpenseDetailDialog extends StatelessWidget {
                                   color: Colors.transparent,
                                   child: InkWell(
                                     onTap: () {
-                                      // TODO: Show full screen image
+                                      showDialog(
+                                        context: context,
+                                        builder: (context) => Dialog(
+                                          backgroundColor: Colors.transparent,
+                                          insetPadding: EdgeInsets.zero,
+                                          child: Stack(
+                                            alignment: Alignment.center,
+                                            children: [
+                                              InteractiveViewer(
+                                                minScale: 0.5,
+                                                maxScale: 4.0,
+                                                child: Image.network(
+                                                  expense.receiptUrl!,
+                                                  fit: BoxFit.contain,
+                                                ),
+                                              ),
+                                              Positioned(
+                                                top: 40,
+                                                right: 20,
+                                                child: IconButton(
+                                                  icon: const Icon(
+                                                    Icons.close,
+                                                    color: Colors.white,
+                                                    size: 30,
+                                                  ),
+                                                  onPressed: () => Navigator.of(
+                                                    context,
+                                                  ).pop(),
+                                                ),
+                                              ),
+                                            ],
+                                          ),
+                                        ),
+                                      );
                                     },
                                   ),
                                 ),