feat(dashboard): optimize teacher dashboard ui and layout

- Refactor layout: move Needs Grading to main column, Homework to sidebar
- Enhance TeacherStats: replace static counts with actionable metrics (Needs Grading, Active Assignments, Avg Score, Submission Rate)
- Update RecentSubmissions: table view with quick grade actions and late status
- Update TeacherSchedule: vertical timeline view with scroll hints
- Update TeacherHomeworkCard: compact list view
- Integrate Recharts: add TeacherGradeTrends chart and shared chart component
- Update documentation

src/modules/homework/data-access.ts

@@ -29,8 +29,69 @@ import type {
   StudentDashboardGradeProps,
   StudentHomeworkScoreAnalytics,
   StudentRanking,
+  TeacherGradeTrendItem,
 } from "./types"
 
+export const getTeacherGradeTrends = cache(async (teacherId: string, limit: number = 5): Promise<TeacherGradeTrendItem[]> => {
+  const recentAssignments = await db.query.homeworkAssignments.findMany({
+    where: and(
+      eq(homeworkAssignments.creatorId, teacherId),
+      or(eq(homeworkAssignments.status, "published"), eq(homeworkAssignments.status, "archived"))
+    ),
+    orderBy: [desc(homeworkAssignments.createdAt)],
+    limit: limit,
+  })
+
+  if (recentAssignments.length === 0) return []
+
+  const assignmentIds = recentAssignments.map((a) => a.id)
+
+  const [maxScoreMap, targetCountRows, submissionStats] = await Promise.all([
+    getAssignmentMaxScoreById(assignmentIds),
+    db
+      .select({
+        assignmentId: homeworkAssignmentTargets.assignmentId,
+        count: count(homeworkAssignmentTargets.studentId),
+      })
+      .from(homeworkAssignmentTargets)
+      .where(inArray(homeworkAssignmentTargets.assignmentId, assignmentIds))
+      .groupBy(homeworkAssignmentTargets.assignmentId),
+    db
+      .select({
+        assignmentId: homeworkSubmissions.assignmentId,
+        avgScore: sql<number>`AVG(${homeworkSubmissions.score})`,
+        count: count(homeworkSubmissions.id),
+      })
+      .from(homeworkSubmissions)
+      .where(
+        and(
+          inArray(homeworkSubmissions.assignmentId, assignmentIds),
+          eq(homeworkSubmissions.status, "graded")
+        )
+      )
+      .groupBy(homeworkSubmissions.assignmentId),
+  ])
+
+  const targetCountMap = new Map<string, number>()
+  for (const r of targetCountRows) targetCountMap.set(r.assignmentId, r.count)
+
+  const statsMap = new Map<string, { avg: number; count: number }>()
+  for (const r of submissionStats) statsMap.set(r.assignmentId, { avg: Number(r.avgScore), count: Number(r.count) })
+
+  return recentAssignments.map((a) => {
+    const stats = statsMap.get(a.id) ?? { avg: 0, count: 0 }
+    return {
+      id: a.id,
+      title: a.title,
+      averageScore: stats.avg,
+      maxScore: maxScoreMap.get(a.id) ?? 0,
+      submissionCount: stats.count,
+      totalStudents: targetCountMap.get(a.id) ?? 0,
+      createdAt: a.createdAt.toISOString(),
+    }
+  }).reverse() // Reverse to show trend from left (older) to right (newer)
+})
+
 const isRecord = (v: unknown): v is Record<string, unknown> => typeof v === "object" && v !== null
 
 const toQuestionContent = (v: unknown): HomeworkQuestionContent | null => {