Introduces standardized tiering system for MCP SDKs based on:
- Specification compliance
- Maintenance quality
- Update frequency

Defines three tiers to help developers choose appropriate SDKs and provide clear improvement pathways for maintainers.

The Icon.sizes field was previously defined as a space-separated string
(e.g., "48x48 96x96"), which was ambiguous and error-prone to parse.

Changed to string[] format (e.g., ["48x48", "96x96"]) for clarity and
consistency. Each size is now a discrete array element, making it easier
to iterate over and validate individual size specifications.

This maintains compatibility with the "any" keyword for scalable formats
while providing a cleaner, more structured representation.

Co-Authored-By: Claude <noreply@anthropic.com>