Add a dropdown menu that allows users to select a library.

app/templates/login.html

@@ -32,6 +32,19 @@
         <label for="port" class="form-label">端口</label>
         <input type="text" class="form-control" id="port" name="port" value="{{ port }}">
     </div>
+    <div class="mb-3">
+        <label for="library_name" class="form-label">音乐库</label>
+        <select class="form-select" id="library_name" name="library_name" {% if not music_libraries %}disabled{% endif %}>
+            {% if music_libraries %}
+            {% for library in music_libraries %}
+            <option value="{{ library }}" {% if selected_library == library %}selected{% endif %}>{{ library }}</option>
+            {% endfor %}
+            {% else %}
+            <option value="" selected>暂无可用的音乐库</option>
+            {% endif %}
+        </select>
+        <div class="form-text">仅显示音乐类型的库，可在连接成功后自动刷新。</div>
+    </div>
     <button type="submit" class="btn btn-primary">连接</button>
 </form>