feat: 라이트/다크 모드 테마 인프라 구축

- ThemeContext.jsx: 테마 상태 관리, localStorage 저장, 시스템 테마 감지
- index.css: CSS 변수 시스템 (다크/라이트 테마 색상)
- tailwind.config.js: darkMode: 'class' 설정
- App.jsx: ThemeProvider 래핑
- Sidebar.jsx: 테마 토글 버튼 (시스템/다크/라이트 순환)

아직 페이지 컴포넌트의 하드코딩 색상 수정 필요

frontend/src/App.jsx

@@ -3,6 +3,7 @@ import { Routes, Route, useLocation } from 'react-router-dom';
 import { AnimatePresence, motion } from 'framer-motion';
 import DeviceLayout, { useIsMobile } from './components/DeviceLayout';
 import Sidebar from './components/Sidebar';
+import { ThemeProvider } from './contexts/ThemeContext';
 import ServerDetail from './pages/ServerDetail';
 import WorldsPage from './pages/WorldsPage';
 import PlayersPage from './pages/PlayersPage';
@@ -46,6 +47,7 @@ function App() {
   // 인증 페이지는 사이드바 없이 렌더링
   if (isAuthPage) {
     return (
+      <ThemeProvider>
       <DeviceLayout>
         <div className="min-h-screen bg-mc-bg text-gray-200 font-sans selection:bg-mc-green/30">
           <div className="absolute inset-0 bg-[url('https://www.transparenttextures.com/patterns/cubes.png')] opacity-[0.03] pointer-events-none"></div>
@@ -58,12 +60,14 @@ function App() {
           </AnimatePresence>
         </div>
       </DeviceLayout>
+      </ThemeProvider>
     );
   }
 
   // 관리자/프로필 페이지는 별도 레이아웃
   if (isStandalonePage) {
     return (
+      <ThemeProvider>
       <DeviceLayout>
         <div className="bg-mc-bg text-gray-200 font-sans selection:bg-mc-green/30">
           <div className="absolute inset-0 bg-[url('https://www.transparenttextures.com/patterns/cubes.png')] opacity-[0.03] pointer-events-none"></div>
@@ -75,10 +79,12 @@ function App() {
           </AnimatePresence>
         </div>
       </DeviceLayout>
+      </ThemeProvider>
     );
   }
 
   return (
+    <ThemeProvider>
     <DeviceLayout>
       <div className="min-h-screen bg-mc-bg text-gray-200 font-sans selection:bg-mc-green/30">
         <div className="absolute inset-0 bg-[url('https://www.transparenttextures.com/patterns/cubes.png')] opacity-[0.03] pointer-events-none"></div>
@@ -105,6 +111,7 @@ function App() {
         </div>
       </div>
     </DeviceLayout>
+    </ThemeProvider>
   );
 }
 

frontend/src/components/Sidebar.jsx

@@ -1,8 +1,9 @@
 import React, { useState, useRef, useEffect } from 'react';
 import { NavLink, useLocation, Link, useNavigate } from 'react-router-dom';
-import { Home, Globe, Users, Menu, X, Gamepad2, Map, Shield, LogIn, LogOut, User, Settings, BarChart2, Package } from 'lucide-react';
+import { Home, Globe, Users, Menu, X, Gamepad2, Map, Shield, LogIn, LogOut, User, Settings, BarChart2, Package, Sun, Moon, Monitor } from 'lucide-react';
 import { motion, AnimatePresence } from 'framer-motion';
 import { useAuth } from '../contexts/AuthContext';
+import { useTheme } from '../contexts/ThemeContext';
 import { io } from 'socket.io-client';
 
 // 사이드바 네비게이션 컴포넌트
@@ -16,6 +17,7 @@ const Sidebar = ({ isMobile = false }) => {
   const location = useLocation();
   const navigate = useNavigate();
   const { isLoggedIn, isAdmin, user, logout, checkAuth } = useAuth();
+  const { theme, cycleTheme, isDark } = useTheme();
   const profileMenuRef = useRef(null);
 
   const menuItems = [
@@ -259,18 +261,18 @@ const Sidebar = ({ isMobile = false }) => {
             initial={{ opacity: 0, scale: 0.9 }}
             animate={{ opacity: 1, scale: 1 }}
             exit={{ opacity: 0, scale: 0.9 }}
-            className="fixed top-1/2 left-1/2 -translate-x-1/2 -translate-y-1/2 w-80 bg-zinc-900 border border-zinc-700 rounded-2xl p-6 z-[101] shadow-2xl"
+            className="fixed top-1/2 left-1/2 -translate-x-1/2 -translate-y-1/2 w-80 bg-[var(--bg-secondary)] border border-[var(--border-color)] rounded-2xl p-6 z-[101] shadow-2xl"
           >
             <div className="text-center">
               <div className="w-12 h-12 mx-auto mb-4 rounded-full bg-red-500/10 border border-red-500/20 flex items-center justify-center">
                 <LogOut className="w-6 h-6 text-red-400" />
               </div>
-              <h3 className="text-lg font-bold text-white mb-2">로그아웃</h3>
-              <p className="text-sm text-zinc-400 mb-6">정말 로그아웃 하시겠습니까?</p>
+              <h3 className="text-lg font-bold text-[var(--text-primary)] mb-2">로그아웃</h3>
+              <p className="text-sm text-[var(--text-secondary)] mb-6">정말 로그아웃 하시겠습니까?</p>
               <div className="flex gap-3">
                 <button
                   onClick={() => setShowLogoutDialog(false)}
-                  className="flex-1 py-2.5 bg-zinc-800 hover:bg-zinc-700 text-zinc-300 rounded-xl font-medium transition-colors"
+                  className="flex-1 py-2.5 bg-[var(--bg-tertiary)] hover:bg-[var(--bg-hover)] text-[var(--text-secondary)] rounded-xl font-medium transition-colors"
                 >
                   취소
                 </button>
@@ -288,6 +290,32 @@ const Sidebar = ({ isMobile = false }) => {
     </AnimatePresence>
   );
 
+  // 테마 토글 버튼 컴포넌트
+  const ThemeToggle = () => {
+    const getThemeIcon = () => {
+      if (theme === 'system') return <Monitor size={18} />;
+      if (theme === 'dark') return <Moon size={18} />;
+      return <Sun size={18} />;
+    };
+    
+    const getThemeLabel = () => {
+      if (theme === 'system') return '시스템';
+      if (theme === 'dark') return '다크';
+      return '라이트';
+    };
+    
+    return (
+      <button
+        onClick={cycleTheme}
+        className="w-full flex items-center gap-3 px-4 py-3 mx-4 mb-2 rounded-xl text-[var(--text-secondary)] hover:text-[var(--text-primary)] hover:bg-[var(--bg-hover)] transition-colors"
+        style={{ width: 'calc(100% - 32px)' }}
+      >
+        {getThemeIcon()}
+        <span className="font-medium">테마: {getThemeLabel()}</span>
+      </button>
+    );
+  };
+
   // 프로필 영역 (클릭 가능)
   const ProfileSection = () => (
     <div className="relative p-4 border-t border-white/10" ref={profileMenuRef}>
@@ -578,6 +606,9 @@ const Sidebar = ({ isMobile = false }) => {
           })}
         </nav>
 
+        {/* 테마 토글 */}
+        <ThemeToggle />
+
         {/* 하단: 로그인/유저 정보 */}
         {isLoggedIn ? (
           <ProfileSection />

frontend/src/contexts/ThemeContext.jsx

@@ -0,0 +1,81 @@
+import React, { createContext, useContext, useState, useEffect } from "react";
+
+// 테마 타입: 'system' | 'dark' | 'light'
+const ThemeContext = createContext();
+
+export const useTheme = () => {
+  const context = useContext(ThemeContext);
+  if (!context) {
+    throw new Error("useTheme must be used within a ThemeProvider");
+  }
+  return context;
+};
+
+export const ThemeProvider = ({ children }) => {
+  // localStorage에서 저장된 테마 가져오기 (기본값: system)
+  const [theme, setTheme] = useState(() => {
+    const saved = localStorage.getItem("theme");
+    return saved || "system";
+  });
+
+  // 실제 적용되는 테마 (시스템 설정 반영)
+  const [resolvedTheme, setResolvedTheme] = useState("dark");
+
+  // 시스템 테마 감지 및 적용
+  useEffect(() => {
+    const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
+
+    const updateResolvedTheme = () => {
+      if (theme === "system") {
+        setResolvedTheme(mediaQuery.matches ? "dark" : "light");
+      } else {
+        setResolvedTheme(theme);
+      }
+    };
+
+    updateResolvedTheme();
+
+    // 시스템 테마 변경 감지
+    const handler = () => updateResolvedTheme();
+    mediaQuery.addEventListener("change", handler);
+
+    return () => mediaQuery.removeEventListener("change", handler);
+  }, [theme]);
+
+  // 테마 클래스를 <html>에 적용
+  useEffect(() => {
+    const root = document.documentElement;
+    root.classList.remove("light", "dark");
+    root.classList.add(resolvedTheme);
+  }, [resolvedTheme]);
+
+  // 테마 변경 및 localStorage 저장
+  const setThemeWithStorage = (newTheme) => {
+    setTheme(newTheme);
+    localStorage.setItem("theme", newTheme);
+  };
+
+  // 테마 순환: system -> dark -> light -> system
+  const cycleTheme = () => {
+    const order = ["system", "dark", "light"];
+    const currentIndex = order.indexOf(theme);
+    const nextIndex = (currentIndex + 1) % order.length;
+    setThemeWithStorage(order[nextIndex]);
+  };
+
+  return (
+    <ThemeContext.Provider
+      value={{
+        theme, // 사용자가 선택한 테마 (system | dark | light)
+        resolvedTheme, // 실제 적용된 테마 (dark | light)
+        setTheme: setThemeWithStorage,
+        cycleTheme,
+        isDark: resolvedTheme === "dark",
+      }}
+    >
+      {children}
+    </ThemeContext.Provider>
+  );
+};
+
+export default ThemeContext;

frontend/src/index.css

@@ -2,14 +2,55 @@
 @tailwind components;
 @tailwind utilities;
 
-/* 기본 html, body 스타일 - 다크 배경 & 스크롤바 레이아웃 고정 */
+/* 테마 CSS 변수 */
+:root {
+  /* 다크 테마 (기본) */
+  --bg-primary: #141414;
+  --bg-secondary: #1c1c1c;
+  --bg-tertiary: #252525;
+  --bg-card: #1c1c1c;
+  --bg-hover: rgba(255, 255, 255, 0.05);
+
+  --text-primary: #ffffff;
+  --text-secondary: #a1a1aa;
+  --text-tertiary: #71717a;
+  --text-muted: #52525b;
+
+  --border-color: rgba(255, 255, 255, 0.1);
+  --border-subtle: rgba(255, 255, 255, 0.05);
+
+  --shadow-color: rgba(0, 0, 0, 0.3);
+}
+
+/* 라이트 테마 */
+.light {
+  --bg-primary: #f8fafc;
+  --bg-secondary: #ffffff;
+  --bg-tertiary: #f1f5f9;
+  --bg-card: #ffffff;
+  --bg-hover: rgba(0, 0, 0, 0.05);
+
+  --text-primary: #18181b;
+  --text-secondary: #52525b;
+  --text-tertiary: #71717a;
+  --text-muted: #a1a1aa;
+
+  --border-color: rgba(0, 0, 0, 0.1);
+  --border-subtle: rgba(0, 0, 0, 0.05);
+
+  --shadow-color: rgba(0, 0, 0, 0.1);
+}
+
+/* 기본 html, body 스타일 */
 html {
   scrollbar-gutter: stable; /* 스크롤바 공간 예약 (세로 스크롤바) */
 }
 
 body {
-  background: #141414;
+  background: var(--bg-primary);
+  color: var(--text-primary);
   min-height: 100vh;
+  transition: background-color 0.3s ease, color 0.3s ease;
 }
 
 /* PC 레이아웃 - min-width 적용 */

frontend/tailwind.config.js

@@ -1,6 +1,7 @@
 /** @type {import('tailwindcss').Config} */
 export default {
   content: ["./index.html", "./src/**/*.{js,ts,jsx,tsx}"],
+  darkMode: "class", // 클래스 기반 다크 모드
   theme: {
     extend: {
       fontFamily: {