test: cover operation SDK query paths

[AlonePenguin]

Purpose

Add a focused, test-only coverage slice for operation external query paths that are separate from the active operation hook/cache PR #242.

/claim #71

Tasks

• Cover executeSDKQuery routing for PostgreSQL, MySQL, Cloudflare D1, Starbase, and Turso with mocked SDK/driver constructors.
• Cover missing external source and unsupported provider guard paths.
• Cover executeExternalQuery falling back to SDK execution when no Outerbase API key is configured.
• Cover the Outerbase API branch preserving object params while normalizing multiline SQL.

Verify

• ./node_modules/.bin/vitest run src/operation-sdk.test.ts src/operation.test.ts --reporter=verbose -> 20 tests passed
• ./node_modules/.bin/prettier --check src/operation-sdk.test.ts -> passed
• git diff --check -> passed

Notes:

• ./node_modules/.bin/vitest run still fails on the existing src/rls/index.test.ts baseline expectations; this new operation slice passes and does not touch RLS.
• ./node_modules/.bin/tsc --noEmit --pretty false still reports existing CDC/cache/DO and src/operation.ts type errors; the new src/operation-sdk.test.ts file is not in the error list.

Before

src/operation.ts SDK connection routing and the no-API-key external query fallback had no focused local coverage in this branch.

After

src/operation-sdk.test.ts exercises those paths without opening real network or database connections.