[P3] chore: review + CI integration

[four-bytes-robby]

Purpose

Add E2E tests to CI pipeline with coverage reporting and quality gates.

Technical Details

• Add test:e2e script to package.json: bun test test/e2e/
• Add test:all script: bun test (runs unit + e2e)
• Coverage: bun test --coverage with lcov output
• CI step: run E2E tests after unit tests
• Coverage threshold: 80% line coverage for E2E suite
• Badge: add coverage badge to README.md

Files to Modify

• package.json — add scripts
• .github/workflows/test.yml — add E2E step (if exists, else create)
• README.md — add coverage badge

Acceptance Criteria

• bun run test:e2e passes locally
• CI runs E2E tests on push/PR
• Coverage report generated
• README shows coverage badge