feat(exams,homework): add rich text exam editor and scan-based grading

- Add Tiptap-based rich text editor with custom extensions (dotted-mark,
  blank-node, image-node, group-block, question-block) for exam creation
- Add AI auto-marking action to convert pasted exam text to structured editor doc
- Add resizable split-panel layout for editor + live preview
- Add student scan upload (photo of paper answers) with drag-drop and reorder
- Add scan image viewer with zoom/rotate/fullscreen for teachers
- Add scan grading view with side-by-side questions and scan images
- Add /teacher/exams/new and /teacher/homework/submissions/[id]/scan-grading routes
- Fix getScansAction to support both teacher (HOMEWORK_GRADE) and student
  (HOMEWORK_SUBMIT) permission scopes
- Add i18n keys for rich editor, scan upload, and scan grading (zh-CN/en)
- Sync architecture diagrams (004/005) with new modules, routes, and deps

src/shared/i18n/messages/zh-CN/exam-homework.json

@@ -123,6 +123,57 @@
       "highErrorWarningDesc": "以下题目错误率超过 70%，建议重点讲解",
       "noData": "暂无分析数据，需等待学生提交并批改后生成",
       "viewAnalytics": "查看分析"
+    },
+    "richEditor": {
+      "title": "富文本组卷",
+      "description": "粘贴试卷文本,使用工具栏标记题目/分组/填空/加点字,右侧实时预览",
+      "basicInfo": "基本信息",
+      "sourceText": "试卷原文",
+      "sourceTextPlaceholder": "在此粘贴完整试卷文本...",
+      "aiAutoMark": "AI 自动标记",
+      "aiMarking": "AI 标记中...",
+      "aiMarkSuccess": "AI 自动标记完成",
+      "aiMarkFailed": "AI 自动标记失败",
+      "aiMarkHint": "粘贴试卷文本后,点击此按钮让 AI 自动识别题目结构",
+      "editorArea": "编辑区",
+      "previewArea": "预览区",
+      "emptyEditor": "请在左侧编辑区输入或粘贴试卷内容",
+      "emptyPreview": "预览将在此处显示",
+      "markQuestion": "标记题目",
+      "markGroup": "标记分组",
+      "markDotted": "加点字",
+      "markBlank": "填空",
+      "insertImage": "插入图片",
+      "questionType": "题型",
+      "score": "分值",
+      "groupTitle": "分组标题",
+      "saveDraft": "保存草稿",
+      "saving": "保存中...",
+      "saveSuccess": "试卷草稿已创建",
+      "saveFailed": "创建失败",
+      "loadFormFailed": "加载表单数据失败",
+      "titleRequired": "请填写试卷标题",
+      "subjectGradeRequired": "请选择科目和年级",
+      "emptyContent": "试卷内容为空",
+      "pasteSourceFirst": "请先粘贴试卷文本",
+      "bold": "加粗",
+      "italic": "斜体",
+      "strike": "删除线",
+      "dotted": "加点字",
+      "bulletList": "无序列表",
+      "orderedList": "有序列表",
+      "quote": "引用",
+      "undo": "撤销",
+      "redo": "重做",
+      "questionTypes": {
+        "single_choice": "单选题",
+        "multiple_choice": "多选题",
+        "true_false": "判断题",
+        "fill_blank": "填空题",
+        "short_answer": "简答题",
+        "essay": "作文题",
+        "text": "文本题"
+      }
     }
   },
   "homework": {
@@ -238,7 +289,18 @@
       "autoSaveSaved": "已自动保存",
       "autoSaveError": "自动保存失败，将在网络恢复后重试",
       "autoSaveRestored": "已从离线缓存恢复未提交的答案",
-      "autoSaveCacheError": "离线缓存恢复失败"
+      "autoSaveCacheError": "离线缓存恢复失败",
+      "scanTitle": "答题拍照上传",
+      "scanDescription": "在纸上作答后,拍照上传整卷答题图片",
+      "selectImageFiles": "请选择图片文件",
+      "uploadFailed": "上传失败",
+      "uploadSuccess": "已上传 {{count}} 张图片",
+      "deleteScan": "删除",
+      "moveUp": "上移",
+      "moveDown": "下移",
+      "dragDropHint": "拖拽图片到此处,或点击选择文件",
+      "pageLabel": "第 {{page}} 页",
+      "scanDisabled": "已提交,无法修改答题图片"
     },
     "grade": {
       "title": "批改",
@@ -286,7 +348,21 @@
       "batchSelectAtLeastOne": "请至少选择一份提交",
       "batchFailed": "批量批改失败",
       "selectAll": "全选",
-      "selectRow": "选择此行"
+      "selectRow": "选择此行",
+      "scanGrading": "阅卷批改",
+      "prevSubmission": "上一份",
+      "nextSubmission": "下一份",
+      "saveGrading": "保存批改",
+      "questionsAndGrading": "题目与批改",
+      "studentScanImages": "学生答题图片",
+      "loadingScans": "加载中...",
+      "loadingImages": "加载答题图片...",
+      "noScans": "暂无答题图片",
+      "saveFailed": "保存失败",
+      "scanFeedbackPlaceholder": "批改评语(可选)...",
+      "scoreOutOf": "/ {{max}} 分",
+      "questionsCount": "题目与批改({{count}} 题)",
+      "scanPagesCount": "学生答题图片({{count}} 页)"
     },
     "review": {
       "title": "复习",