.機能追加、DBバグ修正

web/templates/layouts/base.html

@@ -45,6 +45,9 @@
                     <li class="nav-item">
                         <a class="nav-link" href="/assignments/new"><i class="bi bi-plus-circle me-1"></i>課題登録</a>
                     </li>
+                    <li class="nav-item">
+                        <a class="nav-link" href="/statistics"><i class="bi bi-bar-chart me-1"></i>統計</a>
+                    </li>
                     {{if .isAdmin}}
                     <li class="nav-item">
                         <a class="nav-link" href="/admin/users"><i class="bi bi-people me-1"></i>ユーザー管理</a>