feat: add Intent API Docs

[akbarsaputrait]

No description provided.

[shawnmuggle]

Review Summary

Thank you for adding the Intent API documentation! The new API docs provide comprehensive coverage of the payment system with good examples. However, there are a few issues that should be addressed:

Issues Found:

1. 🚫 DS_Store files: macOS system files are committed that should be removed and added to .gitignore
2. ⚠️ Inconsistent token addresses: Polygon USDC address differs between sections
3. 📝 Broken link: Link text doesn't match filename in API README
4. 💭 Commented code: Solana USDC section is commented out without explanation
5. 📚 Minor improvement: Consider adding error response examples

Positive Aspects:

✅ Comprehensive API documentation with cURL and JavaScript examples
✅ Clear explanation of cross-chain payment routing
✅ Well-structured TypeScript interfaces
✅ Good use of tables for reference data
✅ Helpful "memo required" warnings for Stellar/Solana

Please address the issues above, especially the DS_Store files and the Polygon USDC address inconsistency.

[shawnmuggle]

💡 Good practice to include example error responses would be helpful here. Consider adding an example after the error response format definition:

{
  "data": null,
  "error": {
    "message": "Invalid payment amount",
    "code": "INVALID_AMOUNT"
  },
  "status": 400
}