feat: 书库支持多选批量整理与移除，修正侧栏选中亮条

工具栏新增「选择」模式，卡片显示复选框，工具条提供全选、批量整理与
批量移除。多选时隐藏单卡操作并停用封面阅读入口，避免勾选途中误开
阅读器。全选只覆盖当前筛选结果，切换书架、标签或搜索后会剔除已不
可见的选中项，不对看不见的书执行批量操作。

批量标签用三态复选框：indeterminate 表示部分书持有，跳过即保持原样，
只有明确勾上或取消才统一应用。沿用单本的覆盖语义会静默抹掉其它书
已有的标签。所选书籍分属不同书架时，下拉默认「保持不变」。

侧栏行内的重命名与删除按钮改为绝对定位。此前它们虽然 opacity 为 0，
仍占据 flex 空间，使书架与标签的选中亮条比「全部书籍」窄 47px。书架
列表原为普通 block 无行间距，现与标签列表共用 .library-filter-list，
两处间距一致。

src/ui/index.html

@@ -49,15 +49,17 @@
             <h2>书架</h2>
             <button id="addShelfBtn" class="notes-icon-btn" title="新建书架" aria-label="新建书架">+</button>
           </div>
-          <button class="library-filter active" data-shelf="">全部书籍</button>
-          <button class="library-filter" data-shelf="__uncategorized__">未分类</button>
-          <div id="libraryShelfList"></div>
+          <div class="library-filter-list">
+            <button class="library-filter active" data-shelf="">全部书籍</button>
+            <button class="library-filter" data-shelf="__uncategorized__">未分类</button>
+            <div id="libraryShelfList" class="library-filter-list"></div>
+          </div>
           <div class="library-sidebar-section">
             <div class="library-sidebar-section-head">
               <h3>标签</h3>
               <button id="addTagBtn" class="notes-icon-btn" title="新建标签" aria-label="新建标签">+</button>
             </div>
-            <div id="libraryTagList" class="library-tag-list"></div>
+            <div id="libraryTagList" class="library-filter-list"></div>
           </div>
         </aside>
         <div class="library-content">
@@ -69,9 +71,21 @@
             </div>
             <span id="libStatus" class="status-bar"></span>
             <div class="spacer"></div>
+            <button id="librarySelectModeBtn" class="tb-btn ghost" aria-pressed="false">选择</button>
             <button id="rescanBtn" class="tb-btn ghost">重新扫描</button>
             <button id="addLocalBtn" class="tb-btn">+ 添加本地</button>
           </div>
+          <div id="librarySelectionBar" class="library-selection-bar hidden">
+            <label class="library-select-all">
+              <input type="checkbox" id="librarySelectAll" />
+              <span id="librarySelectAllLabel">全选</span>
+            </label>
+            <span id="librarySelectionCount" class="status-bar">未选择</span>
+            <div class="spacer"></div>
+            <button id="libraryBulkOrganizeBtn" class="tb-btn ghost" disabled>批量整理</button>
+            <button id="libraryBulkRemoveBtn" class="tb-btn danger" disabled>批量移除</button>
+            <button id="librarySelectExitBtn" class="tb-btn ghost">退出选择</button>
+          </div>
           <div id="libGrid" class="grid"></div>
         </div>
       </div>