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/utils.test.ts

@@ -7,6 +7,8 @@ import {
   filterKnowledgePointsByChapter,
   normalizeOptional,
   sortChapters,
+  highlightKnowledgePoints,
+  hasCycleAfterAddingEdge,
 } from "./utils"
 
 // 测试辅助：构造最小合法 Chapter（补齐 createdAt/updatedAt 等必填字段）
@@ -178,4 +180,87 @@ describe("textbooks/utils", () => {
       expect(normalizeOptional("  hello  ")).toBe("hello")
     })
   })
+
+  describe("highlightKnowledgePoints", () => {
+    const makeKp = (id: string, name: string): KnowledgePoint => ({
+      id,
+      name,
+      chapterId: "c1",
+      level: 1,
+      order: 0,
+    })
+
+    it("should return content unchanged when no knowledge points", () => {
+      expect(highlightKnowledgePoints("hello world", [])).toBe("hello world")
+    })
+
+    it("should return content unchanged when content is empty", () => {
+      expect(highlightKnowledgePoints("", [makeKp("1", "test")])).toBe("")
+    })
+
+    it("should wrap single knowledge point name with link", () => {
+      const result = highlightKnowledgePoints("学习物理很有趣", [makeKp("kp1", "物理")])
+      expect(result).toBe("学习[物理](#kp-kp1)很有趣")
+    })
+
+    it("should match case-insensitively", () => {
+      const result = highlightKnowledgePoints("Hello HELLO hello", [makeKp("kp1", "hello")])
+      expect(result).toBe("[Hello](#kp-kp1) [HELLO](#kp-kp1) [hello](#kp-kp1)")
+    })
+
+    it("should match multiple occurrences", () => {
+      const result = highlightKnowledgePoints("物理物理物理", [makeKp("kp1", "物理")])
+      expect(result).toBe("[物理](#kp-kp1)[物理](#kp-kp1)[物理](#kp-kp1)")
+    })
+
+    it("should prioritize longest match (物理学 before 物理)", () => {
+      const kps = [makeKp("kp1", "物理"), makeKp("kp2", "物理学")]
+      const result = highlightKnowledgePoints("物理学是研究物理的学科", kps)
+      // "物理学" 应被 kp2 匹配，独立的 "物理" 应被 kp1 匹配
+      expect(result).toBe("[物理学](#kp-kp2)是研究[物理](#kp-kp1)的学科")
+    })
+
+    it("should handle multiple different knowledge points in one pass", () => {
+      const kps = [makeKp("kp1", "数学"), makeKp("kp2", "物理")]
+      const result = highlightKnowledgePoints("数学和物理都是科学", kps)
+      expect(result).toBe("[数学](#kp-kp1)和[物理](#kp-kp2)都是科学")
+    })
+
+    it("should escape regex metacharacters in knowledge point names", () => {
+      const result = highlightKnowledgePoints("计算 1+2 的结果", [makeKp("kp1", "1+2")])
+      expect(result).toBe("计算 [1+2](#kp-kp1) 的结果")
+    })
+
+    it("should handle knowledge point names with parentheses", () => {
+      const result = highlightKnowledgePoints("函数 f(x) 是映射", [makeKp("kp1", "f(x)")])
+      expect(result).toBe("函数 [f(x)](#kp-kp1) 是映射")
+    })
+  })
+})
+
+describe("textbooks/utils - cycle detection", () => {
+  it("should return false when adding edge to empty graph", () => {
+    const edges: Array<[string, string]> = []
+    expect(hasCycleAfterAddingEdge(edges, "a", "b")).toBe(false)
+  })
+
+  it("should detect direct cycle (a->b then b->a)", () => {
+    const edges: Array<[string, string]> = [["a", "b"]]
+    expect(hasCycleAfterAddingEdge(edges, "b", "a")).toBe(true)
+  })
+
+  it("should detect indirect cycle (a->b->c then c->a)", () => {
+    const edges: Array<[string, string]> = [["a", "b"], ["b", "c"]]
+    expect(hasCycleAfterAddingEdge(edges, "c", "a")).toBe(true)
+  })
+
+  it("should not detect cycle for independent chains", () => {
+    const edges: Array<[string, string]> = [["a", "b"], ["c", "d"]]
+    expect(hasCycleAfterAddingEdge(edges, "b", "c")).toBe(false)
+  })
+
+  it("should not detect cycle for diamond shape", () => {
+    const edges: Array<[string, string]> = [["a", "b"], ["a", "c"], ["b", "d"], ["c", "d"]]
+    expect(hasCycleAfterAddingEdge(edges, "d", "e")).toBe(false)
+  })
 })