refactor: 模块化前端代码 - 将 main.js 和 main.css 拆分为专用模块

- 移除 main.js 并替换为8个 JS 模块
- 移除 main.css 并替换为7个 CSS 模块
- 更新 base.html 以加载模块化文件
- 通过 index.css 保持完全向后兼容
- 改进代码组织、可维护性和可复用性

static/js/utilities.js

@@ -0,0 +1,68 @@
+/**
+ * Service Worker 和其他工具函数
+ */
+
+/**
+ * 注销 Service Worker
+ */
+function unregisterServiceWorker() {
+    if (!("serviceWorker" in navigator)) {
+        return;
+    }
+
+    window.addEventListener("load", () => {
+        navigator.serviceWorker
+            .getRegistrations()
+            .then((registrations) => {
+                registrations.forEach((registration) => {
+                    registration.unregister().then(() => {
+                        console.log("Service Worker unregistered");
+                    });
+                });
+            })
+            .catch((error) => {
+                console.log("Error unregistering Service Worker:", error);
+            });
+
+        // 清理 Service Worker 相关的缓存
+        if ("caches" in window) {
+            caches.keys().then((cacheNames) => {
+                cacheNames.forEach((cacheName) => {
+                    caches.delete(cacheName).then(() => {
+                        console.log("Cache deleted:", cacheName);
+                    });
+                });
+            });
+        }
+    });
+}
+
+/**
+ * 注册模态框处理程序
+ */
+function registerModalHandlers() {
+    const modal = document.getElementById("previewModal");
+    if (!modal) {
+        return;
+    }
+
+    modal.addEventListener("click", (event) => {
+        if (event.target === modal) {
+            closePreview();
+        }
+    });
+
+    document.addEventListener("keydown", (event) => {
+        if (event.key === "Escape" && !isDialogOpen()) {
+            closePreview();
+        }
+    });
+}
+
+/**
+ * 导出到全局作用域
+ */
+window.UtilityFuncs = {
+    unregisterServiceWorker,
+    registerModalHandlers,
+};