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/app/(dashboard)/teacher/homework/submissions/[submissionId]/page.tsx

@@ -1,7 +1,11 @@
 import type { JSX } from "react"
+import Link from "next/link"
 import { notFound } from "next/navigation"
+import { getTranslations } from "next-intl/server"
 import { getHomeworkSubmissionDetails } from "@/modules/homework/data-access"
 import { HomeworkGradingView } from "@/modules/homework/components/homework-grading-view"
+import { Button } from "@/shared/components/ui/button"
+import { ScanLine } from "lucide-react"
 import { formatDate } from "@/shared/lib/utils"
 import {
   AiClientProvider,
@@ -37,6 +41,7 @@ function createAiClientService(): AiClientService {
 
 export default async function HomeworkSubmissionGradingPage({ params }: { params: Promise<{ submissionId: string }> }): Promise<JSX.Element> {
   const { submissionId } = await params
+  const t = await getTranslations("examHomework")
   const submission = await getHomeworkSubmissionDetails(submissionId)
 
   if (!submission) return notFound()
@@ -58,6 +63,12 @@ export default async function HomeworkSubmissionGradingPage({ params }: { params
             <span className="capitalize">Status: {submission.status}</span>
           </div>
         </div>
+        <Button asChild variant="outline" size="sm">
+          <Link href={`/teacher/homework/submissions/${submissionId}/scan-grading`}>
+            <ScanLine className="mr-2 h-4 w-4" />
+            {t("homework.grade.scanGrading")}
+          </Link>
+        </Button>
       </div>
 
       <AiClientProvider service={aiClientService}>