fix(studio): 移除来源卡片悬停 tooltip，失败来源显示报错并可删除

- 去掉来源卡片 hover 时弹出的自定义 tooltip div
- status 为 failed 的来源卡片显示红色报错图标与提示，禁用选中，保留删除按钮

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend-web/src/pages/StudioNotebookDetailPage.tsx

@@ -3,6 +3,7 @@
 import { useCallback, useEffect, useMemo, useRef, useState } from "react";
 import { useParams } from "react-router-dom";
 import {
+  AlertCircle,
   AlignLeft,
   ArrowLeft,
   BookOpen,
@@ -72,14 +73,20 @@ function SourceCard({
 }) {
   const title = item.title ?? item.document?.title ?? "未命名";
   const isProcessing = item.status === "processing";
+  const isFailed = item.status === "failed";
 
   return (
     <div
-      title={title}
-      onClick={() => onToggle(item.id)}
-      className={`group relative flex h-32 w-full cursor-pointer flex-col justify-between rounded-2xl p-4 ring-1 transition-colors ${selected
-          ? "bg-primary/10 ring-primary"
-          : "bg-muted ring-border/50 hover:bg-muted/70"
+      title={isFailed ? `${title}（处理失败）` : title}
+      onClick={() => {
+        if (isFailed) return;
+        onToggle(item.id);
+      }}
+      className={`group relative flex h-32 w-full flex-col justify-between rounded-2xl p-4 ring-1 transition-colors ${isFailed
+          ? "cursor-default bg-destructive/5 ring-destructive/40"
+          : selected
+            ? "cursor-pointer bg-primary/10 ring-primary"
+            : "cursor-pointer bg-muted ring-border/50 hover:bg-muted/70"
         }`}
     >
       {/* 删除按钮 - 右上角始终显示，悬停时高亮 */}
@@ -97,13 +104,15 @@ function SourceCard({
       <div className="flex size-10 items-center justify-center rounded-xl bg-background">
         {isProcessing ? (
           <Loader2 className="size-5 animate-spin text-muted-foreground" />
+        ) : isFailed ? (
+          <AlertCircle className="size-6 text-destructive" />
         ) : (
           <SourceIcon item={item} />
         )}
       </div>
-      <p className="truncate text-xs font-medium text-foreground">{title}</p>
-      <div className="pointer-events-none absolute top-full left-1/2 z-10 mt-2 hidden w-max max-w-[200px] -translate-x-1/2 rounded-lg bg-popover px-3 py-2 text-xs text-popover-foreground shadow-md ring-1 ring-border group-hover:block">
-        {title}
+      <div className="min-w-0">
+        <p className={`truncate text-xs font-medium ${isFailed ? "text-destructive" : "text-foreground"}`}>{title}</p>
+        {isFailed && <p className="mt-0.5 text-[10px] text-destructive/80">处理失败，请删除后重试</p>}
       </div>
     </div>
   );