Use official SingLinkVPN logo on all project covers

[SingLinkLabs]

Summary

• replace the generic shield brand mark with the official SingLinkVPN character logo
• rebuild all eight localized 1600x900 covers and the legacy cover aliases
• keep the security shield illustration while using the real brand identity for the name lockup
• embed an optimized logo copy into generated SVGs
• add regression checks for the official logo and generated covers

Verification

• npm test
• npm audit --audit-level=high
• visual check: English and Simplified Chinese covers
• git diff --check