feat(knowledge): 支持文件导入沉淀知识，知识图谱可视化随主题切换

- 后端新增 /api/knowledge/ingest/file：上传 md/txt/pdf/word/ppt/excel，
  转 Markdown 后走 wiki-capture LLM 蒸馏为陈述式知识笔记，失败回退逐字草稿
- service.capture_file + 文档专用蒸馏提示词，按主题拆分 1~4 页
- 知识图谱导出 HTML 支持 ?theme=light|dark，布局稳定后冻结，
  按度数缩放节点，悬停/点击聚焦邻居
- 前端知识库页新增「导入文件」对话框与 ingestKnowledgeFile API
- 智能体问答页与简介侧边栏 UI 优化；批量人物蒸馏脚本提取正文逻辑修正

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

frontend-web/src/pages/KnowledgeGraphPage.tsx

@@ -4,13 +4,17 @@ import { useNavigate } from "react-router-dom";
 import { toast } from "sonner";
 
 import { Button } from "@/components/ui/button";
+import { useTheme } from "@/contexts/ThemeContext";
 import { knowledgeExportFileUrl } from "@/core/knowledge/api";
 import { useKnowledgeActions } from "@/core/knowledge/hooks";
 
 export default function KnowledgeGraphPage() {
   const navigate = useNavigate();
+  const { theme } = useTheme();
   const { exportGraph } = useKnowledgeActions();
-  const [src, setSrc] = useState<string | null>(null);
+  // Keep the served base URL (without the theme) so a theme toggle can re-skin
+  // the iframe without regenerating the graph on the backend.
+  const [baseSrc, setBaseSrc] = useState<string | null>(null);
   const [stats, setStats] = useState<{ nodes: number; edges: number } | null>(null);
 
   const regenerate = useCallback(async () => {
@@ -18,7 +22,7 @@ export default function KnowledgeGraphPage() {
       const result = await exportGraph.mutateAsync();
       setStats(result.stats);
       // Cache-bust the iframe so it reflects the freshly generated graph.
-      setSrc(`${knowledgeExportFileUrl("graph.html")}?t=${Date.now()}`);
+      setBaseSrc(`${knowledgeExportFileUrl("graph.html")}?t=${Date.now()}`);
     } catch (error) {
       toast.error(error instanceof Error ? error.message : "生成图谱失败");
     }
@@ -29,6 +33,10 @@ export default function KnowledgeGraphPage() {
     void regenerate();
   }, [regenerate]);
 
+  // The graph HTML lives in an iframe and can't read the app's CSS theme, so we
+  // pass the active day/night mode via a query param; toggling re-renders it.
+  const src = baseSrc ? `${baseSrc}&theme=${theme}` : null;
+
   return (
     <div className="flex size-full min-h-0 flex-col">
       <header className="flex items-center gap-2 border-b p-3">