refactor(office): Office 技能统一读取包内 assets，移除包外 office-skills 拷贝与 DSH_BUNDLED_OFFICE_SKILLS

- web-app、sdk-app 的 skill-office 不再覆盖 assetRoot；pythonEnvironment 不变
- Desktop 与 Python SDK 打包不再生成 office-skills 资源目录，删除 prepareOfficeSkillAssets 与 skillSource
- Desktop 打包 smoke 校验 4 个 Office 技能可从运行时归档列出并加载
- 同步测试、README、Agent Note，新增升级指南 office-skill-resources

python/sdk-runtime/src/deepseek_harness_runtime/__init__.py

@@ -176,7 +176,7 @@ def download_office() -> Path:
 
 
 def download_primary_runtime() -> Path:
-    """Download locked CPython, libraries, Node, pnpm and skills into the resource cache.
+    """Download locked CPython, libraries, Node and pnpm into the resource cache.
 
     Return the absolute primary-runtime directory. This is independent of the
     Office engine download and does not copy resources into a Harness home.