docs: add a Sealos one-click deployment guide

Proposal

Add a Sealos one-click deployment guide under docs/docs/deployment/deployment-guides/ and link it from the existing deployment guide index.

The guide would use the same provider-page structure as the current Render, Nhost, DigitalOcean, Koyeb, and Flightcontrol guides.

Deployment evidence

• Template: https://sealos.io/products/app-store/hasura
• Hasura GraphQL Engine: 2.49.5
• Data Connector Agent: 2.49.5
• PostgreSQL: 16.4
• Tested on Sealos: July 28, 2026
• Verified flow: required admin secret, Console access, automatic PostgreSQL source registration, table create and track, row insert and query, restart persistence, health checks, and zero-restart final run

Scope

The PR will change documentation only:

• Add docs/docs/deployment/deployment-guides/sealos.mdx
• Add Sealos to the one-click and full deployment lists in docs/docs/deployment/deployment-guides/index.mdx

The Sealos template is maintained separately, so this repository keeps its existing runtime and installation manifests unchanged.

Maintenance

I can maintain the Sealos deployment path and follow up when Hasura deployment requirements change.