Fix: use explicit None check for Codeforces key highlights update

Co-authored-by: MishkatIT <125080003+MishkatIT@users.noreply.github.com>

Author: Copilot

update_readme.py

@@ -136,7 +136,7 @@ def update_readme(stats):
     )
 
     # Update key highlights if Codeforces is the top platform
-    if stats.get('Codeforces'):
+    if stats.get('Codeforces') is not None:
         cf_count = stats['Codeforces']
         readme_content = re.sub(
             r'(\| )\d+( Problems \|)',