Implement usernames and profile sections

backend/validation.py

@@ -3,7 +3,17 @@ import re
 def is_valid_username(username: str) -> bool:
     if len(username) < 3 or len(username) > 20:
         return False
-    if re.search(r'[\s\u180E\u200B-\u200D\u2060\uFEFF]', username):
+    # Only allow English letters, numbers, dashes and underscores
+    if not re.match(r'^[a-zA-Z0-9_-]+$', username):
+        return False
+    return True
+
+
+def is_valid_display_name(display_name: str) -> bool:
+    if len(display_name) < 1 or len(display_name) > 64:
+        return False
+    # Check if not blank (only whitespace)
+    if not display_name.strip():
         return False
     return True