Dune Analytics MCP Server

# Change: Add Run SQL Tool for Ad-Hoc Queries ## Why Agents need the ability to execute raw, ad-hoc SQL without creating saved queries. This enables dynamic analysis where the agent writes its own SQL to answer unique user questions, supporting an iterative write-run-correct feedback loop. ## What Changes - Add `run_sql` tool to execute raw DuneSQL (Trino dialect) - Support performance tier selection - Apply default row limit of 50 - Add basic SQL validation (non-empty check) ## Impact - Affected specs: adhoc-sql (new capability) - Affected code: server.py (add tool definition) - Dependencies: Requires core-server capability (proposal 1) - **Note**: This empowers agents to act as data analysts