fix: QA report bugs BUG-01 through BUG-11 resolved - streak modal close btn, calculator crash guard, AI chat auto-scroll, leaderboard zero-streak fix, name annotation cleanup everywhere, CBT score display colors, PrepPilot difficulty badge layout

backend/main.py

@@ -8,6 +8,7 @@ from uuid import UUID
 from datetime import datetime, timedelta, date
 from pydantic import BaseModel
 import os
+import re
 
 from database import init_db, get_session
 import models
@@ -838,14 +839,14 @@ def get_leaderboard(
     # Calculate real user's stats
     user_score = 0
     user_accuracy = "0%"
-    user_streak = 1
+    user_streak = 0  # BUG-04 fix: real zero for new users (no artificial min floor)
     if requesting_user:
         if str(requesting_user.id) in DEMO_USER_UUIDS:
             user_score = 9250
             user_accuracy = "88.5%"
             user_streak = requesting_user.streak_count or 25
         else:
-            user_streak = max(1, requesting_user.streak_count)
+            user_streak = requesting_user.streak_count or 0  # BUG-04 fix: 0 is valid
             user_attempts = session.exec(
                 select(models.Attempt).where(
                     models.Attempt.user_id == requesting_user.id,
@@ -871,10 +872,11 @@ def get_leaderboard(
             "isCurrentUser": False,
         })
 
-    # Add the requesting real user
+    # Add the requesting real user — strip role annotations from display name
     if requesting_user:
+        clean_name = re.sub(r'\s*\([^)]*\)\s*$', '', requesting_user.name).strip()
         entries.append({
-            "name": requesting_user.name,
+            "name": clean_name,
             "score": user_score,
             "accuracy": user_accuracy,
             "streak": user_streak,