创作降本：取消同轮retry、两轮history；听书创作/播放分层与前端配套。

Co-authored-by: Cursor <cursoragent@cursor.com>

web/index.html

@@ -201,13 +201,6 @@
           名称
           <input id="input-book-title" type="text" placeholder="未命名作品" maxlength="80" autofocus />
         </label>
-        <label class="field" id="field-creation-mode" hidden>
-          创作方式
-          <select id="input-creation-mode">
-            <option value="dictate" selected>对话落盘（可玩规格）</option>
-            <option value="listen_serial">听书连载（连续消费）</option>
-          </select>
-        </label>
         <input type="hidden" id="input-creation-mode-locked" value="" />
         <div class="dialog-actions">
           <button type="button" class="btn" value="cancel" id="btn-cancel-new">取消</button>