feat: 添加对话应用选择和知识库切换功能

- 新增对话应用管理模块(dify-chat-apps)，支持获取和切换对话应用
- 优化对话应用切换后自动刷新会话列表功能
- 知识库管理页面新增下拉选择器，支持切换不同知识库
- API 层支持 app_id 参数传递，实现多应用会话隔离

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/styles/components/dify-dataset-manager/index.css

@@ -95,6 +95,73 @@
     color: #999;
 }
 
+/* 知识库选择器 */
+.dataset-selector {
+    flex: 1;
+    min-width: 0;
+    overflow: hidden;
+    display: flex;
+    flex-direction: column;
+    gap: 4px;
+}
+
+.dataset-select {
+    width: 100%;
+}
+
+.dataset-select .ant-select-selector {
+    border: 1px solid #e5e5e5 !important;
+    border-radius: 6px !important;
+    background: #fff !important;
+    padding: 2px 8px !important;
+    height: auto !important;
+    min-height: 32px !important;
+}
+
+.dataset-select .ant-select-selection-item {
+    font-weight: 600;
+    font-size: 13px;
+    color: #1a1a1a;
+}
+
+.dataset-select:hover .ant-select-selector {
+    border-color: rgb(0 104 74) !important;
+}
+
+.dataset-select.ant-select-focused .ant-select-selector {
+    border-color: rgb(0 104 74) !important;
+    box-shadow: 0 0 0 2px rgba(0, 104, 74, 0.1) !important;
+}
+
+/* 知识库下拉选项 */
+.dataset-option {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    padding: 4px 0;
+}
+
+.dataset-option-name {
+    flex: 1;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+}
+
+.dataset-option-tag {
+    font-size: 10px;
+    padding: 1px 6px;
+    border-radius: 4px;
+    background: rgba(0, 104, 74, 0.1);
+    color: rgb(0 104 74);
+    white-space: nowrap;
+}
+
+.dataset-option-tag.public {
+    background: rgba(24, 144, 255, 0.1);
+    color: #1890ff;
+}
+
 /* 统计信息 */
 .sidebar-stats {
     padding: 0 16px 16px;