feat(mindspace): 悬浮聊天勾选资料联动、UI 与交互优化

勾选单个文件时 Agent 获知上下文并主动问候；打开悬浮窗使用新会话。
统一弹窗浅色主题、固定高度与输入区布局，支持点击外部收起。

Co-authored-by: Cursor <cursoragent@cursor.com>

src/types.ts

@@ -71,7 +71,20 @@ export type MindSpaceChatContext = {
     id: string;
     displayName: string;
     mimeType: string;
+    filename?: string;
+    sizeBytes?: number;
+    categoryCode?: MindSpaceCategory['code'];
+    assetType?: string;
   };
+  selectedAssets?: Array<{
+    id: string;
+    displayName: string;
+    mimeType: string;
+    filename?: string;
+    sizeBytes?: number;
+    categoryCode?: MindSpaceCategory['code'];
+    assetType?: string;
+  }>;
   homeCategories?: Array<{
     code: MindSpaceCategory['code'];
     name: string;