Sanitize and guard external Stellar explorer links rendered from NFT and commitment metadata

[1nonlypiece]

📌 Description

src/utils/explorerLinks.ts builds external explorer URLs and has a test file,
but metadata-driven links (e.g. from NFT metadata or commitment fields) can flow
into anchors elsewhere. Any externally-sourced URL rendered as a link must be
validated to prevent javascript:/data: schemes and open-redirect/tabnabbing.

This issue hardens external-link rendering across components that consume
metadata, centralizing validation and safe rel/target attributes.

🎯 Requirements and Context

• Add/extend a safeExternalUrl helper that allows only http(s) and known
  explorer hosts; reject other schemes.
• Apply it wherever metadata-derived URLs become anchors (NFT/commitment detail).
• Enforce rel="noopener noreferrer" on all target="_blank" links.
• No regressions to existing explorer-link behaviour.

🛠️ Suggested Execution

1. Fork the repo and create a branch

git checkout -b security/sanitize-external-links

2. Implement changes

• Extend src/utils/explorerLinks.ts with a safeExternalUrl guard and apply it
  in metadata-consuming components.
• Add src/utils/__tests__/safeExternalUrl.test.ts covering allowed hosts,
  rejected schemes (javascript:, data:, vbscript:), and rel/target.
• Add docs/security/EXTERNAL_LINKS.md documenting the allowlist and policy.
• Validate that no unsafe URL can become a clickable link.

3. Test and commit

• Run pnpm test.
• Cover edge cases: protocol-relative URLs, mixed-case schemes, encoded payloads,
  empty/undefined URLs.

Example commit message

security: validate and guard external explorer links from metadata

✅ Guidelines

• Minimum 95% test coverage on new/changed lines.
• Clear, reviewer-friendly documentation.
• Timeframe: 96 hours.

🏷️ Labels

type-security · area-frontend · MAYBE REWARDED · GRANTFOX OSS ·
OFFICIAL CAMPAIGN

💬 Community & Support

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• Introduce yourself before starting so we can avoid duplicate work and pair you
  with a reviewer. Maintainers triage actively and review fast.