Boost title matches in hybrid search

[fa1k3]

Summary

• add a capped title-match boost for hybrid and structured search candidate ordering
• keep final scores bounded while exposing the applied title boost in --explain
• add regression tests for ordering, explain consistency, exact term matching, and common technical separators

Why

Title matches are strong evidence for lookup-style queries. The boost is applied to candidate ordering before final scoring, so it can recover relevant title hits without changing the final score equation or producing scores above 1.0.

Tests

• bun test test/store.helpers.unit.test.ts test/store.test.ts --timeout 60000 --preload ./src/test-preload.ts
• npm run test:node -- test/store.helpers.unit.test.ts test/store.test.ts
• bun run build
• npm run test:types