feat: add retrieval-level temporal scoping

[Helweg]

Summary

• apply date scopes during Usearch traversal rather than after global retrieval
• add blameUntil and scoped filtering for search, peek, and find_similar
• propagate scope across vector, keyword, fusion, reranking, and host schemas

Closes #294

Validation

• npx vitest run tests/native.test.ts tests/database.test.ts tests/search-integration.test.ts tests/mcp-server.test.ts tests/pi-package.test.ts tests/commands.test.ts tests/tools-context.test.ts
• npm run typecheck
• npm run lint
• npm run build && npm run test:run