Merge exams grading into homework

Redirect /teacher/exams/grading* to /teacher/homework/submissions; remove exam grading UI/actions/data-access; add homework student workflow and update design docs.

src/app/(dashboard)/teacher/homework/assignments/[id]/page.tsx

@@ -0,0 +1,79 @@
+import Link from "next/link"
+import { notFound } from "next/navigation"
+import { getHomeworkAssignmentById } from "@/modules/homework/data-access"
+import { Badge } from "@/shared/components/ui/badge"
+import { Button } from "@/shared/components/ui/button"
+import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
+import { formatDate } from "@/shared/lib/utils"
+
+export default async function HomeworkAssignmentDetailPage({ params }: { params: Promise<{ id: string }> }) {
+  const { id } = await params
+  const assignment = await getHomeworkAssignmentById(id)
+
+  if (!assignment) return notFound()
+
+  return (
+    <div className="flex h-full flex-col space-y-8 p-8">
+      <div className="flex flex-col justify-between gap-4 md:flex-row md:items-center">
+        <div>
+          <div className="flex items-center gap-3">
+            <h2 className="text-2xl font-bold tracking-tight">{assignment.title}</h2>
+            <Badge variant="outline" className="capitalize">
+              {assignment.status}
+            </Badge>
+          </div>
+          <p className="text-muted-foreground mt-1">{assignment.description || "—"}</p>
+          <div className="mt-2 text-sm text-muted-foreground">
+            <span>Source Exam: {assignment.sourceExamTitle}</span>
+            <span className="mx-2">•</span>
+            <span>Created: {formatDate(assignment.createdAt)}</span>
+          </div>
+        </div>
+
+        <div className="flex items-center gap-2">
+          <Button asChild variant="outline">
+            <Link href="/teacher/homework/assignments">Back</Link>
+          </Button>
+          <Button asChild>
+            <Link href={`/teacher/homework/assignments/${assignment.id}/submissions`}>View Submissions</Link>
+          </Button>
+        </div>
+      </div>
+
+      <div className="grid gap-4 md:grid-cols-3">
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-sm font-medium text-muted-foreground">Targets</CardTitle>
+          </CardHeader>
+          <CardContent>
+            <div className="text-2xl font-bold">{assignment.targetCount}</div>
+          </CardContent>
+        </Card>
+
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-sm font-medium text-muted-foreground">Submissions</CardTitle>
+          </CardHeader>
+          <CardContent>
+            <div className="text-2xl font-bold">{assignment.submissionCount}</div>
+          </CardContent>
+        </Card>
+
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-sm font-medium text-muted-foreground">Due</CardTitle>
+          </CardHeader>
+          <CardContent>
+            <div className="text-sm">
+              <div className="font-medium">{assignment.dueAt ? formatDate(assignment.dueAt) : "—"}</div>
+              <div className="text-muted-foreground">
+                Late: {assignment.allowLate ? (assignment.lateDueAt ? formatDate(assignment.lateDueAt) : "Allowed") : "Not allowed"}
+              </div>
+            </div>
+          </CardContent>
+        </Card>
+      </div>
+    </div>
+  )
+}
+