chore(release): 准备 v1.16.4-beta.1

[g1331]

Summary

将 package.json 版本同步为 1.16.4-beta.1，为代理生命周期重构后的 beta 预发布做准备。

Related Issue

Related change: #271

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (code improvement without changing functionality)
• Tests (adding or updating tests)
• Build/CI (changes to build system or CI configuration)

Changes

• 更新 package.json 的 version 为 1.16.4-beta.1。
• 版本 tag 将使用 v1.16.4-beta.1，触发 GitHub Release workflow 的 beta 预发布路径。
• 不改变应用代码、数据库 schema 或运行时行为。

Test Plan

• Local tests pass (pnpm test:run)
• Type check passes (pnpm exec tsc --noEmit)
• Lint passes (pnpm lint)
• Manual testing completed

Additional checks for this version-only change: package version parsing and git diff --check passed. The source commit is based on merged master PR #271.

Checklist

• Code follows the project's coding standards
• Tests have been added where necessary
• Documentation has been updated (if applicable)
• Changes do not introduce security vulnerabilities
• Commit messages follow conventions

Screenshots

Not applicable; no UI changes.

Additional Notes

This PR must merge into master before pushing v1.16.4-beta.1; the release workflow rejects tags that are not contained in origin/master. The beta tag will create a prerelease and will not update latest or the rolling MAJOR.MINOR image tag.