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/css/grid.css

@@ -0,0 +1,169 @@
+/**
+ * 网格视图样式
+ */
+
+/* Grid view 容器 */
+.grid-container {
+    display: none;
+    margin-top: 20px;
+    grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
+    gap: 12px;
+}
+
+:root[data-view="grid"] .files-table {
+    display: none;
+}
+
+:root[data-view="grid"] .grid-container {
+    display: grid;
+}
+
+/* 网格卡片 */
+.grid-card {
+    background: var(--container-bg);
+    border: 1px solid var(--border-color);
+    border-radius: 8px;
+    padding: 10px;
+    text-align: center;
+    box-shadow: 0 1px 2px var(--shadow-color);
+}
+
+.grid-checkbox {
+    text-align: left;
+    margin-bottom: 8px;
+}
+
+.grid-checkbox input {
+    transform: scale(1.05);
+    accent-color: var(--link-color);
+}
+
+/* 网格缩略图 */
+.grid-thumb {
+    width: 100%;
+    height: 100px;
+    object-fit: cover;
+    border-radius: 6px;
+    margin-bottom: 8px;
+    background-color: var(--icon-bg);
+    cursor: pointer;
+    transition: transform 0.2s ease, box-shadow 0.2s ease;
+}
+
+.grid-thumb:hover {
+    transform: scale(1.02);
+    box-shadow: 0 2px 8px var(--shadow-color);
+}
+
+/* 网格图标容器 */
+.grid-icon {
+    width: 100%;
+    height: 100px;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    margin-bottom: 8px;
+    border-radius: 6px;
+    background-color: var(--icon-bg);
+    cursor: pointer;
+    transition: transform 0.2s ease, background-color 0.2s ease, box-shadow 0.2s ease;
+}
+
+.grid-icon:hover {
+    transform: scale(1.02);
+    background-color: var(--hover-bg);
+    box-shadow: 0 2px 8px var(--shadow-color);
+}
+
+.grid-icon i {
+    font-size: 64px;
+}
+
+/* 网格卡片文件名 */
+.grid-name {
+    display: block;
+    font-size: 0.95em;
+    color: var(--text-color);
+    margin-bottom: 6px;
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+}
+
+/* 网格卡片操作按钮 */
+.grid-actions {
+    display: flex;
+    gap: 4px;
+    justify-content: center;
+    margin-top: 8px;
+}
+
+.grid-action-btn {
+    background: none;
+    border: none;
+    cursor: pointer;
+    padding: 4px 6px;
+    border-radius: 4px;
+    font-size: 0.85em;
+    transition: all 0.2s ease;
+    display: inline-flex;
+    align-items: center;
+    gap: 3px;
+}
+
+.grid-action-btn.preview {
+    color: var(--link-color);
+}
+
+.grid-action-btn.preview:hover {
+    background-color: rgba(0, 123, 255, 0.1);
+}
+
+.grid-action-btn.download {
+    color: var(--success-color);
+}
+
+.grid-action-btn.download:hover {
+    background-color: rgba(40, 167, 69, 0.1);
+}
+
+.grid-action-btn.delete {
+    color: var(--danger-color);
+}
+
+.grid-action-btn.delete:hover {
+    background-color: rgba(220, 53, 69, 0.1);
+}
+
+@media (max-width: 768px) {
+    .grid-container {
+        grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
+    }
+
+    .grid-icon i {
+        font-size: 48px;
+    }
+}
+
+@media (max-width: 480px) {
+    .grid-container {
+        grid-template-columns: repeat(auto-fill, minmax(120px, 1fr));
+        gap: 8px;
+    }
+
+    .grid-card {
+        padding: 8px;
+    }
+
+    .grid-icon i {
+        font-size: 40px;
+    }
+
+    .grid-name {
+        font-size: 0.9em;
+    }
+
+    .grid-actions {
+        gap: 2px;
+    }
+}