feat: add sidebar project collapse and search

public/index.html

@@ -47,6 +47,10 @@
         <div id="new-chat-dropdown" class="new-chat-dropdown" hidden>
           <button id="import-session-btn">导入本地 CLI 会话</button>
         </div>
+        <div class="session-search">
+          <input id="session-search-input" class="session-search-input" type="search" placeholder="检索会话 / 项目" autocomplete="off" aria-label="检索会话或项目">
+          <button id="session-search-clear" class="session-search-clear" type="button" title="清空检索" aria-label="清空检索" hidden>×</button>
+        </div>
       </div>
       <div id="session-list" class="session-list"></div>
       <div class="sidebar-footer">