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/diag2.mjs

@@ -0,0 +1,42 @@
+// 事件链诊断: node scripts/diag2.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()
+page.on('console', m => console.log(`[页面.${m.type()}]`, m.text().slice(0, 150)))
+await page.goto(`http://localhost:8000/combine?token=${encodeURIComponent(token)}`, { waitUntil: 'networkidle2' })
+await page.waitForSelector('.lib-item')
+await page.click('.lib-item')
+await new Promise(r => setTimeout(r, 600))
+
+const box = await (await page.$('.canvas-box')).boundingBox()
+const cx = box.x + box.width / 2, cy = box.y + box.height / 2
+
+await page.evaluate(() => {
+  window.__md = 0; window.__mu = 0; window.__selEvents = []
+  const cv = document.querySelector('.canvas-box canvas')
+  cv.addEventListener('mousedown', () => window.__md++)
+  cv.addEventListener('mouseup', () => window.__mu++)
+})
+const el = await page.evaluate((x, y) => {
+  const e = document.elementFromPoint(x, y)
+  return e ? `${e.tagName}.${String(e.className).slice(0, 40)}` : 'null'
+}, cx, cy)
+console.log('中心点元素:', el)
+
+await page.mouse.click(cx, cy)
+await new Promise(r => setTimeout(r, 300))
+const st = await page.evaluate(() => ({
+  md: window.__md, mu: window.__mu,
+  sel: window.__ccDebug.getSelected(),
+  units: window.__ccDebug.units(),
+}))
+console.log('事件计数+选中:', JSON.stringify({ md: st.md, mu: st.mu, sel: st.sel }))
+console.log('单元 uid 列表:', JSON.stringify(st.units))
+await browser.close()