docs: refresh existing Sealos deployment links

Proposal

The existing Sealos buttons in README.md and docs/README_zh-CN.md currently point to the legacy template.sealos.io endpoint, which redirects to a regional deployment page.

I would like to refresh those existing links to the canonical template page:

https://sealos.io/products/app-store/pdf2zh

Validation

• Template source: https://github.com/labring-actions/templates/pull/732
• App version: PDFMathTranslate v1.9.11
• Live test date: 2026-07-27
• Verified Gradio login through --authorized
• Completed a real Google English-to-Simplified-Chinese translation
• Generated and downloaded both mono and dual PDF outputs
• Verified provider configuration and API key persistence under /data
• Verified the runtime authentication file is generated with mode 0600 outside the persistent volume
• Deployment credentials stay in deployment-time inputs; the documentation contains no secret values

Smallest candidate diff

I checked the current contribution targets:

• If this maintenance belongs on PDFMathTranslate/PDFMathTranslate:main, the patch changes only the existing URLs in README.md and docs/README_zh-CN.md.
• If it belongs on awwaawwa/PDFMathTranslate:v2-rc, the patch changes only the existing URL in docs/README_zh-CN.md; the v2 root README has no Sealos entry and would remain unchanged.

The proposed change is docs-only and updates an existing provider entry. I can maintain the Sealos deployment path and follow up when the template or documentation needs an update.

@awwaawwa, the contribution guide asks contributors to discuss changes with you during the v2 transition. Please confirm whether this link maintenance is welcome and which target above should receive it.