feat(ai): V2 深度增强 — SSE 流式/全局助手/内容安全/多角色覆盖

对标 Khanmigo/Duolingo Max/Squirrel AI/Century Tech 实现：

- SSE 流式响应：createAiChatCompletionStream AsyncGenerator + /api/ai/chat/stream SSE 端点 + useAiChatStream hook（AbortController 停止生成 + localStorage 持久化）

- Markdown 渲染：AiMarkdownRenderer（react-markdown + remark-gfm + 代码块/表格/列表 + hover 复制按钮）

- 全局 AI 助手：AiAssistantWidget 浮动按钮 + Sheet 侧抽屉 + usePathname 路由推断上下文（7 类场景系统提示）+ dashboard layout 全局注入 AiClientProvider

- 内容安全：content-safety.ts 多层过滤（输入/输出安全过滤 + 每日限制 student 50/teacher 200/parent 30/admin 500 + 学生苏格拉底模式），COPPA/FERPA K12 合规

- 多角色 AI 覆盖：家长端 AiChildSummary（学情摘要）+ 管理员端 AiUsageDashboard（使用监控）+ 学生端 AiStudyPath（个性化学习路径）

- i18n 修复：8 处错误键引用 + zh-CN/en ai.json 全面扩展

- 架构文档 004/005 同步更新

src/modules/ai/services/ai-service.ts

@@ -9,6 +9,8 @@ import {
   QUESTION_VARIANT_SYSTEM_PROMPT,
   SIMILAR_QUESTION_SYSTEM_PROMPT,
   WEAKNESS_ANALYSIS_SYSTEM_PROMPT,
+  CHILD_SUMMARY_SYSTEM_PROMPT,
+  STUDY_PATH_SYSTEM_PROMPT,
 } from "./prompt-templates"
 import { withAiTracking } from "./usage-tracker"
 import {
@@ -17,6 +19,8 @@ import {
   QuestionVariantResultSchema,
   SimilarQuestionListSchema,
   WeaknessAnalysisResultSchema,
+  ChildSummaryResultSchema,
+  StudyPathResultSchema,
 } from "../schema"
 import type {
   AiChatMessage,
@@ -33,6 +37,10 @@ import type {
   SimilarQuestionResult,
   WeaknessAnalysisInput,
   WeaknessAnalysisResult,
+  ChildSummaryInput,
+  ChildSummaryResult,
+  StudyPathInput,
+  StudyPathResult,
 } from "../types"
 
 // ---------------------------------------------------------------------------
@@ -320,6 +328,76 @@ export class DefaultAiService implements AiService {
       return { result: validated.data }
     })
   }
+
+  async generateChildSummary(input: ChildSummaryInput): Promise<ChildSummaryResult> {
+    return withAiTracking(this.userId, "weakness_analysis", undefined, async () => {
+      const userLines = [
+        `Student ID: ${input.studentId}`,
+        input.studentName ? `Student Name: ${input.studentName}` : "",
+        input.grade ? `Grade: ${input.grade}` : "",
+        input.recentGrades && input.recentGrades.length > 0
+          ? `Recent Grades:\n${JSON.stringify(input.recentGrades, null, 2)}`
+          : "",
+        input.attendanceRate !== undefined
+          ? `Attendance Rate: ${(input.attendanceRate * 100).toFixed(1)}%`
+          : "",
+        input.errorBookSummary
+          ? `Error Book Summary:\n${JSON.stringify(input.errorBookSummary, null, 2)}`
+          : "",
+        input.homeworkCompletionRate !== undefined
+          ? `Homework Completion Rate: ${(input.homeworkCompletionRate * 100).toFixed(1)}%`
+          : "",
+      ].filter((line) => line.length > 0)
+      const { content } = await callAi(
+        buildChatMessages(CHILD_SUMMARY_SYSTEM_PROMPT, userLines.join("\n\n")),
+        { temperature: 0.4, maxTokens: 2000 }
+      )
+      const parsed = extractJson(content)
+      const validated = ChildSummaryResultSchema.safeParse(parsed)
+      if (!validated.success) {
+        return {
+          result: {
+            overallAssessment: "Unable to generate summary at this time.",
+            strengths: [],
+            areasForImprovement: [],
+            familyTutoringSuggestions: [],
+            nextSteps: [],
+          },
+        }
+      }
+      return { result: validated.data }
+    })
+  }
+
+  async recommendStudyPath(input: StudyPathInput): Promise<StudyPathResult> {
+    return withAiTracking(this.userId, "weakness_analysis", undefined, async () => {
+      const userLines = [
+        `Student ID: ${input.studentId}`,
+        input.subject ? `Subject: ${input.subject}` : "",
+        input.currentMastery && input.currentMastery.length > 0
+          ? `Current Mastery:\n${JSON.stringify(input.currentMastery, null, 2)}`
+          : "",
+        input.learningGoal ? `Learning Goal: ${input.learningGoal}` : "",
+      ].filter((line) => line.length > 0)
+      const { content } = await callAi(
+        buildChatMessages(STUDY_PATH_SYSTEM_PROMPT, userLines.join("\n\n")),
+        { temperature: 0.5, maxTokens: 2000 }
+      )
+      const parsed = extractJson(content)
+      const validated = StudyPathResultSchema.safeParse(parsed)
+      if (!validated.success) {
+        return {
+          result: {
+            currentLevel: "Analysis unavailable",
+            learningPath: [],
+            summary: "Unable to generate learning path at this time.",
+            motivation: "Keep learning!",
+          },
+        }
+      }
+      return { result: validated.data }
+    })
+  }
 }
 
 /**