Change Summary

Add Biome linting and coverage threshold enforcement as CI quality gates, giving contributors clear standards and proving out the release-please integration (first feat: commit to trigger a release PR).

• Biome v2.4.4 configured with recommended rules, scoped to src/**/*.ts
• Coverage thresholds (85% stmts, 80% branches, 80% functions, 85% lines) with src/index.ts excluded
• CI updated with parallel lint/typecheck/test jobs gating the build
• Existing code fixed — unused imports/variables, non-null assertions replaced with ?? 0, import sorting

Risk & Impact Assessment

Risk Level: low

• Biome is a dev-only dependency — no runtime impact
• Coverage thresholds are set ~5% below current actuals to allow normal code evolution
• All existing tests pass unchanged (92/92)
• Source code changes are mechanical (import sorting, ! → ?? 0)

Test Plan

• npm run lint — passes clean (0 errors, 0 warnings)
• npx tsc --noEmit — passes clean
• npx vitest run --coverage — 92 tests pass, all thresholds met
• npm run build — passes clean

Manual Verification Steps

1. Pull the branch and run npm ci
2. Run npm run lint — should pass with no findings
3. Run npx vitest run --coverage — verify thresholds are enforced and all pass
4. Intentionally break a lint rule (e.g., add an unused import) and run npm run lint — should fail
5. After merge, verify release-please creates a release PR on main

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