Add SQD Portal MCP under Blockchain Data

[karelxfi]

This PR adds the official SQD Portal MCP server (maintained by subsquid-labs) under the Blockchain Data section.

• One entry, placed at the end of the Blockchain Data section (the section is append-ordered, not alphabetical), matching the surrounding en-dash format.
• Repo: https://github.com/subsquid-labs/portal-mcp-server
• A multi-chain onchain-data server wrapping the SQD Portal API across EVM, Solana, Bitcoin, Substrate, and Hyperliquid (logs, transactions, token transfers, OHLC, wallet summaries, analytics).
• Runs as a hosted Streamable HTTP endpoint (https://portal.sqd.dev/mcp) and locally over stdio.

This is a maintainer submission.