Dune Analytics MCP Server

# Change: Add MCP Resources with dune:// URI Scheme ## Why MCP Resources provide passive, read-only data access that is semantically distinct from tool execution. Exposing cached query results as resources enables zero-credit data access and allows agents to "watch" execution states without repeated tool calls. ## What Changes - Register custom `dune://` URI scheme handler - Add `dune://query/{query_id}/latest` resource for cached results (zero credits) - Add `dune://query/{query_id}/sql` resource for query SQL definition - Add `dune://execution/{execution_id}/status` resource for execution state ## Impact - Affected specs: mcp-resources (new capability) - Affected code: server.py (add resource definitions) - Dependencies: Requires core-server capability (proposal 1) - **Benefit**: Cached result access consumes no execution credits