fix: v2.6 组合画布选中根因修复+右键菜单+3D 三场景

- 选中失效根因: Vue3 布尔 prop 缺省转换(editable 缺省→false)
  withDefaults 默认 true 修复, 左键选中/右键选中/菜单动作全链路打通
- 右键菜单: 右键单元弹操作菜单(顺/逆旋转/镜像/底边对齐/删除)
  动作 emit('ctx') 由父组件统一执行, document 级委托
- 3D 三场景: 室内(窗后墙+木地板)/室外(外墙+草地)/影棚(网格)
  场景联动背景色, 真实浏览器截图验证三场景渲染
- 菜单动作行为级验证: 旋转后 1600x1800 宽高互换✓ 删除清空✓

frontend/scripts/vei-check.mjs

@@ -0,0 +1,34 @@
+// Vue 监听器挂载诊断: node scripts/vei-check.mjs <token>
+import puppeteer from 'puppeteer-core'
+const EDGE = 'C:/Program Files (x86)/Microsoft/Edge/Application/msedge.exe'
+const token = process.argv[2]
+const browser = await puppeteer.launch({
+  executablePath: EDGE,
+  headless: 'new',
+  args: ['--window-size=1440,900', '--enable-unsafe-swiftshader', '--use-gl=angle', '--use-angle=swiftshader'],
+  defaultViewport: { width: 1440, height: 900 },
+})
+const page = await browser.newPage()
+await page.goto(`http://localhost:8000/combine?token=${encodeURIComponent(token)}`, { waitUntil: 'networkidle2' })
+await page.waitForSelector('.lib-item')
+await page.click('.lib-item')
+await new Promise(r => setTimeout(r, 500))
+const box = await (await page.$('.canvas-box')).boundingBox()
+await page.mouse.click(box.x + box.width / 2, box.y + box.height / 2, { button: 'right' })
+await new Promise(r => setTimeout(r, 300))
+const res = await page.evaluate(() => {
+  const items = document.querySelectorAll('.ctx-item')
+  if (!items.length) return { err: '菜单不存在' }
+  const el = items[items.length - 1]
+  const vei = el._vei
+  const out = {
+    veiKeys: vei ? Object.keys(vei) : null,
+    itemText: el.textContent.trim().slice(0, 12),
+    inCcWrap: !!el.closest('.cc-wrap'),
+  }
+  el.click()
+  return out
+})
+console.log(JSON.stringify(res, null, 1))
+await new Promise(r => setTimeout(r, 400))
+await browser.close()