feat: v1.4 组合画布旋转编辑+方向核验+双向门符号

- 组合画布旋转编辑: 选中单元 ⟲/⟳ 90°旋转(绕几何中心)
  分割线法向与开向角度同步旋转, 水平镜像(开向镜像)
- 数据方向核验: 以31729/31740真实图纸比对确认2D渲染Y向正确
- 2D渲染补双向开启门虚线交叉符号(wtf)
- Node数学验证: 旋转后宽高互换/法向转轴/可逆性全部通过

frontend/src/views/CombineView.vue

@@ -25,6 +25,16 @@
           <div class="head-row">
             <span>组合画布（{{ units.length }} 个单元 · 拖动摆放 · 边缘自动吸附）</span>
             <div style="display:flex; gap:8px; align-items:center">
+              <el-tooltip content="选中单元逆时针旋转90°" placement="top">
+                <el-button size="small" :disabled="!selectedUid" @click="canvasRef?.rotateUnit(selectedUid!, -90)">⟲ 90°</el-button>
+              </el-tooltip>
+              <el-tooltip content="选中单元顺时针旋转90°" placement="top">
+                <el-button size="small" :disabled="!selectedUid" @click="canvasRef?.rotateUnit(selectedUid!, 90)">⟳ 90°</el-button>
+              </el-tooltip>
+              <el-tooltip content="选中单元水平镜像" placement="top">
+                <el-button size="small" :disabled="!selectedUid" @click="canvasRef?.mirrorUnit(selectedUid!)">⇋ 镜像</el-button>
+              </el-tooltip>
+              <el-divider direction="vertical" />
               <el-button size="small" :disabled="!selectedUid" @click="alignBottom">底边对齐</el-button>
               <el-button size="small" :disabled="!selectedUid" type="danger" plain @click="deleteSelected">删除单元</el-button>
               <el-button size="small" :disabled="!shapes.length" @click="clearAll">清空</el-button>