feat: PWA 기본 설정 (manifest, service worker, 앱 아이콘)

- manifest.json: 앱 이름 "청춘약국 마일리지", standalone 모드, 보라색 테마
- sw.js: 정적 자산 캐싱 (동적 페이지 제외)
- 앱 아이콘 192x192, 512x512 PNG 생성
- /sw.js 루트 라우트로 서비스 워커 scope 허용

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/static/sw.js

@@ -0,0 +1,63 @@
+const CACHE_NAME = 'chungchun-pharmacy-v1';
+const STATIC_ASSETS = [
+  '/static/js/lottie.min.js',
+  '/static/animations/ai-loading.json',
+  '/static/icons/icon-192.png',
+  '/static/icons/icon-512.png'
+];
+
+// Install: pre-cache static assets
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then((cache) => cache.addAll(STATIC_ASSETS))
+  );
+  self.skipWaiting();
+});
+
+// Activate: clean old caches
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then((keys) =>
+      Promise.all(
+        keys.filter((key) => key !== CACHE_NAME).map((key) => caches.delete(key))
+      )
+    )
+  );
+  self.clients.claim();
+});
+
+// Fetch: cache-first for static, network-only for dynamic
+self.addEventListener('fetch', (event) => {
+  const url = new URL(event.request.url);
+
+  // Skip non-GET requests
+  if (event.request.method !== 'GET') return;
+
+  // Skip dynamic routes entirely
+  if (url.pathname.startsWith('/api/') ||
+      url.pathname.startsWith('/admin') ||
+      url.pathname.startsWith('/claim') ||
+      url.pathname.startsWith('/my-page') ||
+      url.pathname === '/privacy' ||
+      url.pathname === '/logout' ||
+      url.pathname === '/') {
+    return;
+  }
+
+  // Cache-first for static assets and fonts
+  if (url.pathname.startsWith('/static/') ||
+      url.hostname === 'fonts.googleapis.com' ||
+      url.hostname === 'fonts.gstatic.com') {
+    event.respondWith(
+      caches.match(event.request).then((cached) => {
+        return cached || fetch(event.request).then((response) => {
+          if (response.ok) {
+            const clone = response.clone();
+            caches.open(CACHE_NAME).then((cache) => cache.put(event.request, clone));
+          }
+          return response;
+        });
+      })
+    );
+  }
+});