test: add allowlist unit coverage

[023dominus-coder]

Refs #71

Summary

Adds focused Vitest coverage for the SQL allowlist module.

What changed

• Adds src/allowlist/index.test.ts.
• Covers disabled allowlist, admin bypass, AST-normalized allowed queries with trailing semicolon, rejected-query audit inserts, and empty SQL errors.

Validation

Could not run Vitest locally in this environment because pnpm, npm, bun, and npx are not available on PATH and node_modules is not installed.

The test follows existing project patterns from src/cache/index.test.ts and uses vi.fn() mocks for the datasource RPC.

Bounty

Issue: #71

Label: Bounty / Rewarded