fix(office): PDF 导出后不再渲染，合并 DSH_BUNDLED_PRIMARY_RUNTIME 到 DSH_PRIMARY_RUNTIME

- office 路由技能：PDF 导出写明验收（复制的文件非空且以 `%PDF-` 开头）并在此停止；保留排版类任务主动渲染。office 工具让渲染只差一次调用后，模型常在导出后渲染 result.pdf 验收，e2e「exports PDF」因此失败。
- office-pptx / office-xlsx 删去不提供操作的免责句。
- Desktop、SDK 与 web-app 配置只读 DSH_PRIMARY_RUNTIME，空值视为未设置；SDK 启动器在用户未设置时才填入下载缓存路径。
- e2e 断言附带工具调用诊断；render 检测改用记录的 office 调用，新增 render-context.spec.ts。
- 同步 office 快照、README 与升级指南。

python/sdk-runtime/runtime-bootstrap.mjs

@@ -89,11 +89,12 @@ if (resource !== undefined) {
   Reflect.deleteProperty(process.env, 'DSH_PTC_RUNTIME_NODE')
   await import('@deepseek-ai/dsh-ptc-runtime-node/process')
 } else if (selection === undefined) {
+  // A user-set DSH_PRIMARY_RUNTIME, including the empty opt-out, takes precedence over the downloaded cache.
   if (cache !== undefined && existsSync(join(cache, 'primary', 'complete'))) {
-    process.env.DSH_BUNDLED_PRIMARY_RUNTIME = join(cache, 'primary', 'primary-runtime')
+    process.env.DSH_PRIMARY_RUNTIME ??= join(cache, 'primary', 'primary-runtime')
   }
   let packageManager
-  const primary = process.env.DSH_PRIMARY_RUNTIME ?? process.env.DSH_BUNDLED_PRIMARY_RUNTIME
+  const primary = process.env.DSH_PRIMARY_RUNTIME
   if (primary !== undefined && primary !== '') {
     const { resolvePrimaryRuntime } = await import('@deepseek-ai/dsh-tool-workspace-dependencies')
     const { node, pnpm } = await resolvePrimaryRuntime(primary)