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/components/ui/resizable-panel.tsx

@@ -0,0 +1,78 @@
+"use client"
+
+import { useCallback, useEffect, useRef, useState, type ReactNode } from "react"
+import { cn } from "@/shared/lib/utils"
+
+interface ResizablePanelProps {
+  /** 左侧最小宽度百分比 */
+  minLeft?: number
+  /** 右侧最小宽度百分比 */
+  minRight?: number
+  /** 初始左侧宽度百分比 */
+  initialLeft?: number
+  left: ReactNode
+  right: ReactNode
+  className?: string
+}
+
+/**
+ * 可拖拽分栏容器(左右两栏,中间分隔条可拖拽调整宽度)。
+ * 自实现,无新依赖。用于试卷编辑器左编辑右预览、阅卷式批改左题目右图片等场景。
+ */
+export function ResizablePanel({
+  minLeft = 20,
+  minRight = 20,
+  initialLeft = 50,
+  left,
+  right,
+  className,
+}: ResizablePanelProps) {
+  const [leftPct, setLeftPct] = useState(initialLeft)
+  const containerRef = useRef<HTMLDivElement>(null)
+  const draggingRef = useRef(false)
+
+  const onPointerDown = useCallback((e: React.PointerEvent) => {
+    e.preventDefault()
+    draggingRef.current = true
+    document.body.style.cursor = "col-resize"
+    document.body.style.userSelect = "none"
+  }, [])
+
+  useEffect(() => {
+    const onMove = (e: PointerEvent) => {
+      if (!draggingRef.current || !containerRef.current) return
+      const rect = containerRef.current.getBoundingClientRect()
+      const pct = ((e.clientX - rect.left) / rect.width) * 100
+      const clamped = Math.min(100 - minRight, Math.max(minLeft, pct))
+      setLeftPct(clamped)
+    }
+    const onUp = () => {
+      draggingRef.current = false
+      document.body.style.cursor = ""
+      document.body.style.userSelect = ""
+    }
+    window.addEventListener("pointermove", onMove)
+    window.addEventListener("pointerup", onUp)
+    return () => {
+      window.removeEventListener("pointermove", onMove)
+      window.removeEventListener("pointerup", onUp)
+    }
+  }, [minLeft, minRight])
+
+  return (
+    <div ref={containerRef} className={cn("flex h-full w-full", className)}>
+      <div style={{ width: `${leftPct}%` }} className="h-full min-w-0 overflow-hidden">
+        {left}
+      </div>
+      <div
+        role="separator"
+        aria-orientation="vertical"
+        onPointerDown={onPointerDown}
+        className="w-1.5 shrink-0 cursor-col-resize bg-border transition-colors hover:bg-primary/40"
+      />
+      <div style={{ width: `${100 - leftPct}%` }} className="h-full min-w-0 overflow-hidden">
+        {right}
+      </div>
+    </div>
+  )
+}