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

src/components/AI/AITutorChat.tsx

@@ -1,6 +1,6 @@
 "use client"
 
-import { useState } from "react"
+import { useState, useRef, useEffect } from "react"
 import { Card, CardContent, CardHeader, CardTitle, CardFooter } from "@/components/ui/card"
 import { Button } from "@/components/ui/button"
 import { Input } from "@/components/ui/input"
@@ -39,6 +39,15 @@ export function AITutorChat() {
   const [input, setInput] = useState('');
   const [isOpen, setIsOpen] = useState(false);
   const [isExpanded, setIsExpanded] = useState(false);
+  // BUG-03 fix: ref to anchor bottom of chat for auto-scroll
+  const bottomRef = useRef<HTMLDivElement>(null);
+
+  // Auto-scroll to latest message whenever messages change
+  useEffect(() => {
+    if (bottomRef.current) {
+      bottomRef.current.scrollIntoView({ behavior: 'smooth' });
+    }
+  }, [messages]);
 
   const handleSend = () => {
     if (!input.trim()) return;
@@ -118,6 +127,8 @@ export function AITutorChat() {
             </div>
           </div>
         ))}
+        {/* BUG-03 fix: invisible scroll anchor */}
+        <div ref={bottomRef} />
       </CardContent>
       
       <CardFooter className="p-4 border-t border-border bg-background shrink-0">