feat(data): add new membership fees entry to finances

Added entry for membership fees in July to track additional revenue correctly. This update ensures financial data completeness and accuracy. No functional changes to the application's logic.

data/finances.json

@@ -36,6 +36,11 @@
             "Bank Fees": {
                 "EUR": -49.05
             }
+        },
+        "7": {
+            "Membership Fees": {
+                "EUR": 20
+            }
         }
     }
 }