feat: 引入多渠道发布策略

- 创建staging分支用于beta发布
- 新增alpha发布工作流(.github/workflows/alpha.yml)
- 新增beta发布工作流(.github/workflows/beta.yml)
- 添加release:alpha和release:beta脚本
- 为渐进式迁移奠定基础设施

🔄 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -33,6 +33,8 @@
     "changeset:status": "changeset status",
     "release": "pnpm changeset publish",
     "release:snapshot": "pnpm changeset version --snapshot snapshot && pnpm changeset publish --tag snapshot",
+    "release:alpha": "pnpm changeset version --snapshot alpha && pnpm changeset publish --tag alpha",
+    "release:beta": "pnpm changeset version --snapshot beta && pnpm changeset publish --tag beta",
     "version:patch": "pnpm changeset add --type patch",
     "version:minor": "pnpm changeset add --type minor",
     "version:major": "pnpm changeset add --type major"