feat(textbooks): 知识图谱功能全面重构 — 前置依赖 + dagre 布局 + React Flow 可视化 + 师生双视角

将教材模块图谱从基本无用状态升级为完整知识图谱可视化系统。

数据层：新增 knowledgePointPrerequisites 表（复合主键+双外键 cascade）；新增 data-access-graph.ts（server-only）知识点关联聚合、学生/班级掌握度查询；utils.ts 新增 hasCycleAfterAddingEdge（DFS 循环依赖检测）。

业务层：3 个新 Server Action（getKnowledgeGraphDataAction 三视图模式、createPrerequisiteAction 含循环检测、deletePrerequisiteAction）；graph-layout.ts 重写为 dagre 分层有向图布局。

视图层：knowledge-graph.tsx 重写为 React Flow 主组件（全书视图+搜索高亮+关联节点高亮+章节着色）；4 个新组件（graph-kp-node/graph-prerequisite-edge/graph-toolbar/graph-node-detail-panel）；use-graph-data.ts 派生值模式避免 effect 中 setState。

架构：严格三层架构，客户端通过 Server Action 间接访问 server-only 数据层；权限校验+ i18n 全覆盖；架构文档 004/005 同步。

测试：utils.test.ts 新增 5 个循环检测测试，graph-layout.test.ts 重写 5 个 dagre 布局测试，全部 30 个教材模块单元测试通过。

附带提交 drizzle/0005 error-book 迁移文件以保持 journal 一致性。

src/modules/textbooks/components/graph-toolbar.tsx

@@ -0,0 +1,86 @@
+"use client"
+
+import { useTranslations } from "next-intl"
+import { Search, RotateCcw } from "lucide-react"
+import { Button } from "@/shared/components/ui/button"
+import { Input } from "@/shared/components/ui/input"
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/shared/components/ui/select"
+import type { GraphViewMode } from "../types"
+
+interface GraphToolbarProps {
+  viewMode: GraphViewMode
+  onViewModeChange: (mode: GraphViewMode) => void
+  availableViewModes: GraphViewMode[]
+  searchText: string
+  onSearchChange: (text: string) => void
+  onResetView: () => void
+}
+
+const ALL_VIEW_MODES: readonly GraphViewMode[] = [
+  "structure",
+  "student-mastery",
+  "class-mastery",
+]
+
+function isGraphViewMode(value: string): value is GraphViewMode {
+  return ALL_VIEW_MODES.some((mode) => mode === value)
+}
+
+export function GraphToolbar({
+  viewMode,
+  onViewModeChange,
+  availableViewModes,
+  searchText,
+  onSearchChange,
+  onResetView,
+}: GraphToolbarProps) {
+  const t = useTranslations("textbooks")
+
+  const handleValueChange = (v: string): void => {
+    if (isGraphViewMode(v)) {
+      onViewModeChange(v)
+    }
+  }
+
+  return (
+    <div className="flex flex-wrap items-center gap-2 p-2 border-b bg-background/95 shrink-0">
+      <Select value={viewMode} onValueChange={handleValueChange}>
+        <SelectTrigger className="w-[140px] h-8 text-xs">
+          <SelectValue />
+        </SelectTrigger>
+        <SelectContent>
+          {availableViewModes.includes("structure") && (
+            <SelectItem value="structure">{t("graph.viewMode.structure")}</SelectItem>
+          )}
+          {availableViewModes.includes("student-mastery") && (
+            <SelectItem value="student-mastery">{t("graph.viewMode.studentMastery")}</SelectItem>
+          )}
+          {availableViewModes.includes("class-mastery") && (
+            <SelectItem value="class-mastery">{t("graph.viewMode.classMastery")}</SelectItem>
+          )}
+        </SelectContent>
+      </Select>
+
+      <div className="relative flex-1 min-w-[120px]">
+        <Search className="absolute left-2 top-1/2 -translate-y-1/2 h-3 w-3 text-muted-foreground" />
+        <Input
+          value={searchText}
+          onChange={(e) => onSearchChange(e.target.value)}
+          placeholder={t("graph.toolbar.search")}
+          className="h-8 pl-7 text-xs"
+        />
+      </div>
+
+      <Button variant="outline" size="sm" className="h-8 px-2" onClick={onResetView}>
+        <RotateCcw className="h-3 w-3 mr-1" />
+        <span className="text-xs">{t("graph.toolbar.resetView")}</span>
+      </Button>
+    </div>
+  )
+}