test(hybrid): exercise FilterExpression form of vsimFilter in integration

[banker]

Summary

Closes #20. The type widening (vsimFilter: string | FilterExpression), the renderFilter() plumbing, the unit-test coverage of both forms, and the docs update all landed during PR #9's review cycle. This PR fills the last remaining acceptance criterion from the issue: an integration test that drives the typed DSL form through FT.HYBRID against a real Redis 8.4+ container.

• New test inside the existing vsimFilter (pre-filter on vector candidates) describe block.
• Composes Tag('category').eq('furniture').and(Num('price').lt(400)) to confirm DSL composition renders correctly to Redis's filter dialect.
• Reuses the "gibberish text → only the VSIM side runs" isolation strategy from the existing string-form test, so the assertion truly pins vsimFilter behavior.

Test plan

• npm run type-check:tests — clean
• npx vitest run tests/integration/hybrid-search.test.ts — 9/9 passing (8 pre-existing + 1 new)
• CI green

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds missing integration coverage for the FilterExpression (typed filter DSL) form of HybridQuery.vsimFilter by driving FT.HYBRID against a real Redis 8.4+ instance, closing the final acceptance criterion from #20.

Changes:

• Imports the typed filter DSL helpers (Tag, Num) into the hybrid integration test suite.
• Adds an integration test verifying vsimFilter accepts a composed FilterExpression and correctly gates VSIM-side candidates (using the existing “gibberish text” isolation strategy).

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