Unify SingLinkVPN brand naming

[SingLinkLabs]

Summary

• standardize the English brand name as SingLinkVPN
• standardize Simplified Chinese as 星连VPN
• standardize Traditional Chinese as 星連VPN
• update public documentation, metadata, citation data, schema labels, and GitHub Pages content

Validation

• publication guard passed for 44 public files
• 4 unit tests passed
• 62 relative links passed
• benchmark CSV validation passed
• JSON and YAML validation passed
• no legacy spaced brand names remain

Scope

Documentation and public metadata only. No product source code, credentials, node configuration, payment code, or backend logic is included.