Add base2sol interactive frontend to Base-Solana bridge docs

[mrtdlgc]

Summary

• Adds a "Try an interactive frontend" section to the Base-Solana bridge quickstart.
• Links to the deployed base2sol frontend and source repository.
• Notes that base2sol is community-maintained and non-custodial.
• Adds a safety reminder to verify token contract addresses, Solana mint addresses, recipients, and wallet prompts before signing.

Contribution fit

This keeps the change inside the existing Base-Solana bridge quickstart instead of adding a new top-level section or standalone third-party guide. The addition is focused on the existing Base-Solana bridge flow and links to source for review.

Validation

• Verified https://base2sol.xyz returns HTTP 200.
• Verified https://base2sol.xyz/skill.md is served.
• Ran git diff --check.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2