test: cover StarbaseDB handler route gates

[jorgeschulz]

Summary

/claim #71

Adds a focused handler route coverage slice for StarbaseDB without changing production behavior:

• covers /status/database dialect metadata from the real Hono route
• verifies disabled export and import feature gates leave routes unregistered and return 404
• verifies import/export routes are blocked for external data sources before dispatching body parsing/export logic
• verifies internal import route dispatch reaches the dump import content-type validation

This is intentionally separate from the active CSV/import/export/worker/plugin/operation coverage PRs.

Verification

• COREPACK_ENABLE_AUTO_PIN=0 pnpm exec vitest --run src/handler.routes.test.ts -> 6 tests passed
• COREPACK_ENABLE_AUTO_PIN=0 pnpm exec prettier --check src/handler.routes.test.ts -> passed
• git diff --check -> passed
• COREPACK_ENABLE_AUTO_PIN=0 pnpm exec vitest --run -> existing baseline still has 4 unrelated failures in src/rls/index.test.ts; this new test file passes in that full run.

Transparency: AI-assisted with Codex; diff reviewed and verified locally.