Fix: 미사용 import 제거, fetch_live_messages 이중 DB 호출 캐싱

- app.py: normalize_user_text 미사용 import 제거
- db.py: fetch_live_messages에 @st .cache_data(ttl=5) 추가
교사 대시보드+채팅보드 이중 호출 → 5초 캐시로 1회만 쿼리

https://claude.ai/code/session_018WXW8M8SMsWcHtj1RynUi4

app.py

@@ -11,7 +11,7 @@ from db import (
 )
 from config import APP_CSS, MAX_STUDENT_NAME_LEN
 from utils import get_client_ip, get_kst_now_str, log_audit
-from validators import normalize_user_text, validate_opinion_content, validate_student_name
+from validators import validate_opinion_content, validate_student_name
 from views.home import render_home_page
 from views.lobby import render_lobby_page
 from views.admin import render_admin_page

db.py

@@ -329,9 +329,10 @@ def fetch_topic_data(supabase: Client, room_name):
 # [5] 토론(debate) 관련 쿼리
 # ==========================================
 
-def fetch_live_messages(supabase: Client, room_name, limit):
+@st.cache_data(ttl=5)
+def fetch_live_messages(_supabase: Client, room_name, limit):
     res = execute_query(
-        supabase.table("debate").select("*").eq("room_name", room_name).order("id", desc=True).limit(limit),
+        _supabase.table("debate").select("*").eq("room_name", room_name).order("id", desc=True).limit(limit),
         fail_message="🚨 데이터 불러오기 실패",
     )
     if not res or not res.data: