[EPIC] MVP Implementation

**Objective**

Implement the MVP subscription system based on the design and architecture document, including the Asset and AssetRegistry smart contracts with all subscription flows (Subscribe, Get Subscription, View Subscription, and Revoke Subscription).

**Estimation**

**Dependencies**

Depends on #2 (Design core flows and architecture)

Start with the design and architecture document from dependency #2, then identify the planned Asset and AssetRegistry contracts. Use the specified Subscribe, Get Subscription, View Subscription, and Revoke Subscription flows as the scope; done means implementing the MVP subscription system with all four flows.

Written by the indexing model from the issue text.