fix: Asia/Seoul 타임존 지원을 위해 luxon 라이브러리 도입

- backend/routes/todos.js: 오늘의 할일 조회 시 KST 기준으로 날짜 계산
- backend/routes/schedules.js: 주간/월간 일정 조회 시 KST 기준으로 날짜 범위 계산
- backend/routes/bible.js: 오늘의 성경 구절 조회 시 KST 기준으로 날짜 계산
- flutter_app: Mock 데이터 사용 시 타임존 관련 주석 추가

backend/routes/bible.js

@@ -1,8 +1,12 @@
 const express = require("express");
+const { DateTime } = require("luxon");
 const BibleVerse = require("../models/BibleVerse");
 
 const router = express.Router();
 
+// Korea Standard Time zone
+const KST_TIMEZONE = "Asia/Seoul";
+
 const pickRandomVerse = async (filter) => {
   const results = await BibleVerse.aggregate([
     { $match: filter },
@@ -13,7 +17,9 @@ const pickRandomVerse = async (filter) => {
 
 router.get("/today", async (req, res) => {
   try {
-    const targetDate = req.query.date || new Date().toISOString().slice(0, 10);
+    // Get today's date in KST (YYYY-MM-DD format)
+    const todayKst = DateTime.now().setZone(KST_TIMEZONE).toISODate();
+    const targetDate = req.query.date || todayKst;
     const datedVerse = await pickRandomVerse({
       active: true,
       date: targetDate,

backend/routes/schedules.js

@@ -1,31 +1,35 @@
 const express = require("express");
+const { DateTime } = require("luxon");
 const Schedule = require("../models/Schedule");
 
 const router = express.Router();
 
-const startOfWeek = (date = new Date()) => {
-  const copy = new Date(date);
-  const day = copy.getDay();
-  const diff = day === 0 ? -6 : 1 - day;
-  copy.setDate(copy.getDate() + diff);
-  copy.setHours(0, 0, 0, 0);
-  return copy;
+// Korea Standard Time zone
+const KST_TIMEZONE = "Asia/Seoul";
+
+const startOfWeek = () => {
+  // Get current time in KST and find the start of the week (Monday)
+  const nowKst = DateTime.now().setZone(KST_TIMEZONE);
+  // Luxon uses 1 = Monday, 7 = Sunday
+  const startOfWeekKst = nowKst.startOf("week"); // Monday 00:00:00.000
+  return startOfWeekKst.toJSDate();
 };
 
-const endOfWeek = (date = new Date()) => {
-  const start = startOfWeek(date);
-  const end = new Date(start);
-  end.setDate(end.getDate() + 6);
-  end.setHours(23, 59, 59, 999);
-  return end;
+const endOfWeek = () => {
+  // Get current time in KST and find the end of the week (Sunday)
+  const nowKst = DateTime.now().setZone(KST_TIMEZONE);
+  const endOfWeekKst = nowKst.endOf("week"); // Sunday 23:59:59.999
+  return endOfWeekKst.toJSDate();
 };
 
-const startOfMonth = (date = new Date()) => {
-  return new Date(date.getFullYear(), date.getMonth(), 1, 0, 0, 0, 0);
+const startOfMonth = () => {
+  const nowKst = DateTime.now().setZone(KST_TIMEZONE);
+  return nowKst.startOf("month").toJSDate();
 };
 
-const endOfMonth = (date = new Date()) => {
-  return new Date(date.getFullYear(), date.getMonth() + 1, 0, 23, 59, 59, 999);
+const endOfMonth = () => {
+  const nowKst = DateTime.now().setZone(KST_TIMEZONE);
+  return nowKst.endOf("month").toJSDate();
 };
 
 router.get("/", async (req, res) => {

backend/routes/todos.js

@@ -1,27 +1,26 @@
 const express = require("express");
+const { DateTime } = require("luxon");
 const Todo = require("../models/Todo");
 
 const router = express.Router();
 
-// Get day range in Korea Standard Time (UTC+9)
+// Korea Standard Time zone
+const KST_TIMEZONE = "Asia/Seoul";
+
+// Get day range in Korea Standard Time (Asia/Seoul)
 const getDayRange = () => {
-  const now = new Date();
-  // Get current time in KST (UTC+9)
-  const kstOffset = 9 * 60; // minutes
-  const utcTime = now.getTime() + (now.getTimezoneOffset() * 60000);
-  const kstTime = new Date(utcTime + (kstOffset * 60000));
+  // Get current time in KST
+  const nowKst = DateTime.now().setZone(KST_TIMEZONE);
 
-  // Start of day in KST
-  const startKst = new Date(kstTime);
-  startKst.setHours(0, 0, 0, 0);
+  // Start of day in KST (00:00:00.000)
+  const startOfDayKst = nowKst.startOf("day");
 
-  // End of day in KST
-  const endKst = new Date(kstTime);
-  endKst.setHours(23, 59, 59, 999);
+  // End of day in KST (23:59:59.999)
+  const endOfDayKst = nowKst.endOf("day");
 
-  // Convert back to UTC for MongoDB query
-  const start = new Date(startKst.getTime() - (kstOffset * 60000));
-  const end = new Date(endKst.getTime() - (kstOffset * 60000));
+  // Convert to JavaScript Date objects (UTC) for MongoDB query
+  const start = startOfDayKst.toJSDate();
+  const end = endOfDayKst.toJSDate();
 
   return { start, end };
 };