Replace admin dashboard stub with real stats

- 4 stat cards: students (+monthly), courses (published), active enrollments (expiring alert), homework pending
- Recent enrollments list (last 8)
- Top courses by enrollment count
- Activity counters: total lessons completed, total homework submitted
- All cards link to relevant admin pages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/admin/dashboard/page.tsx

@@ -1,27 +1,202 @@
+import { prisma } from "@/lib/prisma";
 import Link from "next/link";
 
-export default function AdminDashboard() {
+export default async function AdminDashboard() {
+  const now = new Date();
+  const weekAgo = new Date(now.getTime() - 7 * 24 * 60 * 60 * 1000);
+  const monthAgo = new Date(now.getTime() - 30 * 24 * 60 * 60 * 1000);
+
+  const [
+    totalStudents,
+    newStudentsMonth,
+    totalCourses,
+    publishedCourses,
+    activeEnrollments,
+    expiringWeek,
+    homeworkPending,
+    homeworkTotal,
+    progressTotal,
+  ] = await Promise.all([
+    prisma.user.count({ where: { role: "student" } }),
+    prisma.user.count({ where: { role: "student", createdAt: { gte: monthAgo } } }),
+    prisma.course.count(),
+    prisma.course.count({ where: { published: true } }),
+    prisma.courseEnrollment.count({
+      where: { OR: [{ expiresAt: null }, { expiresAt: { gt: now } }] },
+    }),
+    prisma.courseEnrollment.count({
+      where: { expiresAt: { gt: now, lte: new Date(now.getTime() + 7 * 24 * 60 * 60 * 1000) } },
+    }),
+    prisma.homeworkSubmission.count({ where: { feedbacks: { none: {} } } }),
+    prisma.homeworkSubmission.count(),
+    prisma.lessonProgress.count(),
+  ]);
+
+  // Recent enrollments
+  const recentEnrollments = await prisma.courseEnrollment.findMany({
+    orderBy: { enrolledAt: "desc" },
+    take: 8,
+    include: {
+      user: { select: { name: true, email: true } },
+      course: { select: { title: true } },
+    },
+  });
+
+  // Most active courses (by enrollment count)
+  const topCourses = await prisma.course.findMany({
+    where: { published: true },
+    include: { _count: { select: { enrollments: true, modules: true } } },
+    orderBy: { enrollments: { _count: "desc" } },
+    take: 5,
+  });
+
   return (
-    <div className="p-8">
-      <h1 className="text-2xl font-semibold text-slate-800 mb-1">Обзор</h1>
-      <p className="text-slate-500 mb-8">Управление платформой Second Brain.</p>
-      <div className="grid grid-cols-1 md:grid-cols-3 gap-4">
-        <Link href="/admin/courses" className="bg-white rounded-2xl border border-slate-200 p-6 hover:border-amber-300 transition-colors">
-          <p className="text-3xl mb-2">📚</p>
-          <p className="font-medium text-slate-800">Курсы</p>
-          <p className="text-sm text-slate-400 mt-1">Управление контентом</p>
+    <div className="p-8 max-w-5xl">
+      <h1 className="text-2xl font-bold mb-1">Обзор</h1>
+      <p className="text-sm mb-8" style={{ color: "var(--muted-foreground)" }}>
+        Платформа Second Brain · {now.toLocaleDateString("ru-RU", { day: "numeric", month: "long", year: "numeric" })}
+      </p>
+
+      {/* Stats grid */}
+      <div className="grid grid-cols-2 md:grid-cols-4 gap-4 mb-8">
+        <StatCard
+          label="Студентов"
+          value={totalStudents}
+          sub={`+${newStudentsMonth} за месяц`}
+          href="/admin/users"
+        />
+        <StatCard
+          label="Курсов"
+          value={totalCourses}
+          sub={`${publishedCourses} опубликовано`}
+          href="/admin/courses"
+        />
+        <StatCard
+          label="Активных доступов"
+          value={activeEnrollments}
+          sub={expiringWeek > 0 ? `${expiringWeek} истекает на неделе` : "нет истекающих"}
+          subAccent={expiringWeek > 0}
+          href="/admin/courses"
+        />
+        <StatCard
+          label="ДЗ на проверку"
+          value={homeworkPending}
+          sub={`${homeworkTotal} всего сдано`}
+          subAccent={homeworkPending > 0}
+          href="/curator/homework"
+        />
+      </div>
+
+      <div className="grid md:grid-cols-2 gap-6">
+        {/* Recent enrollments */}
+        <div className="card-aubade p-5">
+          <div className="flex items-center justify-between mb-4">
+            <p className="text-xs font-bold uppercase tracking-widest" style={{ color: "var(--muted-foreground)" }}>
+              Последние зачисления
+            </p>
+            <Link href="/admin/users" className="text-xs underline" style={{ color: "var(--muted-foreground)" }}>
+              Все →
             </Link>
-        <Link href="/admin/users" className="bg-white rounded-2xl border border-slate-200 p-6 hover:border-amber-300 transition-colors">
-          <p className="text-3xl mb-2">👥</p>
-          <p className="font-medium text-slate-800">Пользователи</p>
-          <p className="text-sm text-slate-400 mt-1">Управление доступом</p>
+          </div>
+          {recentEnrollments.length === 0 ? (
+            <p className="text-sm" style={{ color: "var(--muted-foreground)" }}>Нет зачислений</p>
+          ) : (
+            <div className="space-y-2">
+              {recentEnrollments.map((e) => (
+                <div key={`${e.userId}-${e.courseId}`} className="flex items-center gap-3 text-sm">
+                  <div className="flex-1 min-w-0">
+                    <p className="font-medium truncate">{e.user.name}</p>
+                    <p className="text-xs truncate" style={{ color: "var(--muted-foreground)" }}>{e.course.title}</p>
+                  </div>
+                  <span className="text-xs shrink-0" style={{ color: "var(--muted-foreground)" }}>
+                    {new Date(e.enrolledAt).toLocaleDateString("ru-RU")}
+                  </span>
+                </div>
+              ))}
+            </div>
+          )}
+        </div>
+
+        {/* Top courses + progress stat */}
+        <div className="space-y-6">
+          <div className="card-aubade p-5">
+            <div className="flex items-center justify-between mb-4">
+              <p className="text-xs font-bold uppercase tracking-widest" style={{ color: "var(--muted-foreground)" }}>
+                Популярные курсы
+              </p>
+              <Link href="/admin/courses" className="text-xs underline" style={{ color: "var(--muted-foreground)" }}>
+                Все →
               </Link>
-        <div className="bg-white rounded-2xl border border-slate-200 p-6 opacity-50">
-          <p className="text-3xl mb-2">📊</p>
-          <p className="font-medium text-slate-800">Аналитика</p>
-          <p className="text-sm text-slate-400 mt-1">Этап 10</p>
+            </div>
+            {topCourses.length === 0 ? (
+              <p className="text-sm" style={{ color: "var(--muted-foreground)" }}>Нет курсов</p>
+            ) : (
+              <div className="space-y-3">
+                {topCourses.map((c) => (
+                  <div key={c.id} className="flex items-center gap-3 text-sm">
+                    <div className="flex-1 min-w-0">
+                      <p className="font-medium truncate">{c.title}</p>
+                      <p className="text-xs" style={{ color: "var(--muted-foreground)" }}>
+                        {c._count.modules} модулей
+                      </p>
+                    </div>
+                    <div className="text-right shrink-0">
+                      <p className="font-bold">{c._count.enrollments}</p>
+                      <p className="text-xs" style={{ color: "var(--muted-foreground)" }}>студентов</p>
+                    </div>
+                  </div>
+                ))}
+              </div>
+            )}
+          </div>
+
+          <div className="card-aubade p-5">
+            <p className="text-xs font-bold uppercase tracking-widest mb-3" style={{ color: "var(--muted-foreground)" }}>
+              Активность
+            </p>
+            <div className="flex items-end gap-6">
+              <div>
+                <p className="text-3xl font-bold">{progressTotal}</p>
+                <p className="text-xs mt-0.5" style={{ color: "var(--muted-foreground)" }}>уроков пройдено</p>
+              </div>
+              <div>
+                <p className="text-3xl font-bold">{homeworkTotal}</p>
+                <p className="text-xs mt-0.5" style={{ color: "var(--muted-foreground)" }}>работ сдано</p>
+              </div>
+            </div>
+          </div>
         </div>
       </div>
     </div>
   );
 }
+
+function StatCard({
+  label,
+  value,
+  sub,
+  subAccent,
+  href,
+}: {
+  label: string;
+  value: number;
+  sub?: string;
+  subAccent?: boolean;
+  href?: string;
+}) {
+  const content = (
+    <div className="card-aubade p-4">
+      <p className="text-3xl font-bold">{value}</p>
+      <p className="text-xs font-bold uppercase tracking-widest mt-1" style={{ color: "var(--muted-foreground)" }}>
+        {label}
+      </p>
+      {sub && (
+        <p className="text-xs mt-1.5" style={{ color: subAccent ? "oklch(0.577 0.245 27.325)" : "var(--muted-foreground)" }}>
+          {sub}
+        </p>
+      )}
+    </div>
+  );
+
+  return href ? <Link href={href}>{content}</Link> : content;
+}