feat: 初始版本，圆角主题与首次管理员引导

app/templates/activities/detail.html

@@ -0,0 +1,7 @@
+{% extends 'base.html' %}
+{% block title %}活动详情{% endblock %}
+{% block content %}
+<h3>{{ activity.title }}</h3>
+<p>{{ activity.description }}</p>
+<a class="btn btn-primary" href="{{ url_for('activities.submit', act_id=activity.id) }}">投稿</a>
+{% endblock %}