feat(admin): add admin panel with user management, daily puzzle CRUD, and activity graph

- Add admin page at /admin (restricted to ADMIN_EMAIL via proxy)
- Implement user ban/unban and deletion
- Add daily puzzle creation, modification, deletion
- Include 14-day activity chart with hover details
- Add User.banned field to schema and migrate database
- Block banned users from logging in
- Add ADMIN_EMAIL to .env.local configuration
- Update Prisma client after schema changes

app/api/admin/daily/[id]/route.ts

@@ -0,0 +1,25 @@
+import { NextResponse } from "next/server";
+import { prisma } from "../../../../../lib/prisma";
+
+type Params = { params: Promise<{ id: string }> };
+
+// PATCH /api/admin/daily/[id] — modifier un puzzle
+export async function PATCH(req: Request, { params }: Params) {
+  const { id } = await params;
+  const { startArticle, targetArticle } = await req.json() as {
+    startArticle: string;
+    targetArticle: string;
+  };
+  const puzzle = await prisma.dailyPuzzle.update({
+    where: { id },
+    data: { startArticle, targetArticle },
+  });
+  return NextResponse.json(puzzle);
+}
+
+// DELETE /api/admin/daily/[id] — supprimer un puzzle
+export async function DELETE(_req: Request, { params }: Params) {
+  const { id } = await params;
+  await prisma.dailyPuzzle.delete({ where: { id } });
+  return NextResponse.json({ ok: true });
+}