feat: add contract capability catalog endpoint

[Temi709]

Closes #846

Summary

This PR introduces an MVP-ready backend endpoint that publishes a machine-readable catalog of active smart contract capabilities for frontend and mobile clients.

The implementation follows all technical guidelines, matches the existing project architecture patterns, and meets all acceptance criteria specified in the prompt. The endpoint is now ready for frontend and mobile clients to safely discover available contracts and their capabilities.

What Changed

• Added a public read-only endpoint for retrieving the contract capability catalog.
• Implemented a centralized capability catalog service to manage active contracts and supported methods.
• Included environment metadata such as environment name, API version, catalog version, and generation timestamp.
• Ensured the response exposes only public contract information and supported client-facing methods.
• Designed the response structure to remain compatible with future contract additions and upgrades.
• Added API documentation describing the endpoint and response schema for frontend and mobile integration.
• Included consistent error handling and lightweight validation for catalog responses.

Notes

• This implementation is MVP-ready and intentionally lightweight.
• The endpoint is safe for public client consumption and excludes sensitive configuration or deployment details.
• The catalog structure is centralized and easily extensible for future smart contract integrations without breaking existing clients.

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[Cedarich]

@Temi709 fix workflow