#416 Persistent SQLite connection for MCP calls #419

Problem

SQLite connection is opened, PRAGMAs set, and migrations run on every cora brain / MCP call (~10-15ms overhead).

Location

src/index/mod.rs:31-41 via src/mcp/tools.rs:395-403

Solution

Use OnceLock<Connection> or a connection pool for the MCP server process.

Expected Impact

Save 10-15ms per search call.