feat: 添加学员详情/方案编辑/方案列表新页面

- student.html: 学员详情页，支持编辑/添加/删除问题
- plan_edit.html: 方案编辑页
- plans.html: 方案列表页
- home.html: 首页

app/templates/home.html

@@ -0,0 +1,46 @@
+{% extends "base.html" %}
+
+{% block title %}首页 - 钢琴练习方案系统{% endblock %}
+
+{% block content %}
+<div class="row g-4 mb-4">
+    <div class="col-md-4">
+        <div class="card text-center h-100">
+            <div class="card-body">
+                <i class="bi bi-people text-primary fs-1"></i>
+                <h2 class="mt-2">{{ student_count }}</h2>
+                <p class="text-muted">学员</p>
+                <a href="/students" class="btn btn-outline-primary btn-sm">查看</a>
+            </div>
+        </div>
+    </div>
+    <div class="col-md-4">
+        <div class="card text-center h-100">
+            <div class="card-body">
+                <i class="bi bi-collection text-success fs-1"></i>
+                <h2 class="mt-2">{{ class_count }}</h2>
+                <p class="text-muted">班级</p>
+                <a href="/classes" class="btn btn-outline-success btn-sm">查看</a>
+            </div>
+        </div>
+    </div>
+    <div class="col-md-4">
+        <div class="card text-center h-100">
+            <div class="card-body">
+                <i class="bi bi-clipboard-check text-warning fs-1"></i>
+                <h2 class="mt-2">{{ plan_count }}</h2>
+                <p class="text-muted">方案</p>
+                <a href="/plans" class="btn btn-outline-warning btn-sm">查看</a>
+            </div>
+        </div>
+    </div>
+</div>
+
+<div class="card">
+    <div class="card-body text-center py-5">
+        <i class="bi bi-music-note-beamed text-muted" style="font-size: 48px;"></i>
+        <h4 class="mt-3 text-muted">欢迎使用钢琴练习方案管理系统</h4>
+        <p class="text-muted">从左侧菜单选择功能</p>
+    </div>
+</div>
+{% endblock %}