Add total litter collected display to user profile

- Updated backend userService to calculate total litter collected across all attended events
- Added totalLitterCollected field to UserProfile interface
- Added new statistics card showing total litter collected in kg
- Updated profile grid layout to accommodate 5 statistics cards
- Displays litter collected with 1 decimal place precision

src/services/api.ts

@@ -46,11 +46,24 @@ export class ApiClient {
     });
 
     if (!response.ok) {
-      const error: ApiError = await response.json();
+      let error: ApiError;
+      try {
+        error = await response.json();
+      } catch {
+        // If response is not JSON, create a generic error
+        throw new Error(`HTTP ${response.status}: ${response.statusText}`);
+      }
       throw new Error(error.message || 'An error occurred');
     }
 
-    return response.json();
+    // Handle empty responses (like DELETE)
+    const contentType = response.headers.get('content-type');
+    if (contentType && contentType.includes('application/json')) {
+      return response.json();
+    }
+    
+    // For non-JSON responses, return empty object
+    return {} as T;
   }
 
   async get<T>(endpoint: string, options?: RequestInit): Promise<T> {