feat: upgrade version to v1.6.0 (#939)

* feat: upgrade version to v1.6.0

- Update version number to 1.6.0 in all package.json files
- Add v1.6.0 placeholder in CHANGELOG.md and CHANGELOG_EN.md

* docs: update release skill to use bilingual format (zh + en collapsed)

* chore: upgrade dependencies

* fix: correct CHANGELOG placeholder position and update version-upgrade skill

* docs: update version-upgrade skill with correct CHANGELOG placeholder position

.claude/skills/release/SKILL.md

@@ -17,7 +17,8 @@ description: Create a GitHub release for cloudflare_temp_email project. Use when
    ```
    Sort by PR number ascending.
 4. **Compose release body**: Follow the template in [references/release-template.md](references/release-template.md). Key rules:
-   - Copy changelog sections verbatim (Features, Bug Fixes, Testing, Improvements). Omit empty sections.
+   - Write release body in **bilingual format**: Chinese sections first (from `CHANGELOG.md`), then wrap the English sections (from `CHANGELOG_EN.md`) in `<details><summary>English</summary>...</details>`.
+   - Copy changelog sections verbatim from both files. Omit empty sections.
    - Wrap PRs list in `<details><summary>PRs</summary>...</details>`.
    - Always include the cache-clearing discussion link.
    - End with `**Full Changelog**` comparison link.

.claude/skills/version-upgrade/SKILL.md

@@ -30,7 +30,7 @@ description: 升级项目版本号。当用户要求升级版本、更新版本
 
 ## CHANGELOG 格式
 
-中文 (CHANGELOG.md) - 在 `## v{OLD_VERSION}(main)` 之前插入：
+中文 (CHANGELOG.md) - 在 `## v{OLD_VERSION}(main)` 之前插入（即语言切换链接 `</p>` 之后）：
 ```markdown
 ## v{VERSION}(main)