docs: add Sealos one-click deploy

[yangchuansheng]

Summary

This PR adds Sealos as an optional third-party installation path for Glance.

Why this is useful

• Lowers friction for self-hosting and evaluation
• Keeps existing manual deployment instructions intact
• Does not change runtime behavior for existing users

What changed

• Added Sealos to the existing Other installation list, alongside entries such as Coolify.io
• Added a dedicated docs/sealos.md page with the Deploy on Sealos button and setup notes
• Linked to https://sealos.io/products/app-store/glance
• Documented template defaults, storage review, and post-deploy verification

Reviewability

• Docs-only change
• No referral, affiliate, or tracking links
• Deployment definition is maintained in the Sealos templates repository at template/glance/index.yaml
• Required inputs to review: generated template defaults and any user-provided inputs in Sealos
• Persistence/storage note: The template includes persistence/storage resources; reviewers should check the referenced template before production use.

Validation

• Checked the Sealos App Store URL format
• Checked README, docs, and PR text for common secret and referral patterns
• Confirmed the docs mention inputs, persistence/storage, and post-deploy steps