fix: 제출 버튼 3초 비활성화로 Rate Limiting 단순화

DB 쿼리 방식 제거, session_state + disabled 파라미터로 교체.
제출 성공 후 3초간 버튼이 회색으로 비활성화됨.
name 'time' is not defined 오류도 함께 수정.

https://claude.ai/code/session_01BRbPoMBBfvgN58bGkNhmv7

app.py

@@ -1,4 +1,5 @@
 import logging
+import time
 
 import streamlit as st
 
@@ -8,7 +9,6 @@ from db import (
     fetch_live_messages,
     fetch_topic_data,
     init_db,
-    is_recent_submission,
     submit_opinion,
     using_service_role_key,
 )
@@ -140,7 +140,8 @@ with col_stt:
         height=120,
     )
 
-if st.button("의견 제출", use_container_width=True, type="primary"):
+_submit_cooldown = time.time() - st.session_state.get('last_submit_ts', 0) < 3
+if st.button("의견 제출", use_container_width=True, type="primary", disabled=_submit_cooldown):
     input_ok, safe_input, input_error_code, input_error_message = validate_opinion_content(user_input, max_len=700)
     student_ok, safe_student_name, student_error_code, student_error_message = validate_student_name(student_name, max_len=MAX_STUDENT_NAME_LEN)
     student_number_ok, safe_student_number, _, student_number_error_message = validate_student_name(student_number, max_len=20)
@@ -153,15 +154,11 @@ if st.button("의견 제출", use_container_width=True, type="primary"):
         now = get_kst_now_str()
         author_role_for_submit = "교사" if user_role == "교사" else "학생"
         client_ip = get_client_ip()
-        if is_recent_submission(supabase, room_name, safe_student_name):
-            st.warning("⏳ 15초 후 다시 제출할 수 있습니다.")
-            st.stop()
         insert_payload = {
             "room_name": room_name, "timestamp": now, "student_name": safe_student_name,
             "content": safe_input, "sentiment": sentiment, "author_role": author_role_for_submit,
         }
         if debate_ip_column_available() and client_ip:
-            # inet 컬럼이므로 유효한 IP 형식 유지 — 마지막 옥텟만 0으로 익명화
             parts = client_ip.split(".")
             anonymized_ip = f"{parts[0]}.{parts[1]}.{parts[2]}.0" if len(parts) == 4 else None
             if anonymized_ip: