test: cover sql macros plugin

[gebibd00-jpg]

/claim #71

Summary

• Add focused Vitest coverage for plugins/sql-macros/index.ts.
• Cover plugin initialization, middleware config capture, no-data-source passthrough, admin SELECT * passthrough, current parser fallback behavior, $_exclude expansion for internal sources, external-source passthrough, and pragma query passthrough.

Validation

• pnpm exec vitest run plugins/sql-macros/index.test.ts -> 8 tests passed
• pnpm exec prettier --check plugins/sql-macros/index.test.ts -> passed
• git diff --check -> passed

This is a test-only coverage slice with no production behavior changes.