Add frontend tests and CI pipeline step

[kivo360]

Problem

The CI pipeline (.github/workflows/ci.yml) only runs backend checks (ruff lint). There are:

• No frontend lint step in CI
• No frontend build verification in CI
• No frontend unit tests at all (no test files found in frontend/)

What to do

Phase 1: CI pipeline

1. Add pnpm lint step to CI
2. Add pnpm build step to CI (catches TypeScript errors)

Phase 2: Test infrastructure

1. Set up Vitest (or Jest) for the frontend
2. Add test configuration to frontend/package.json
3. Create initial test files for critical components

Phase 3: Component tests

Priority components to test:

• Command page spec submission flow
• Onboarding wizard step transitions
• Spec workspace phase switching
• WebSocket event handling

Difficulty: Medium | Skill: Frontend (Vitest/Jest, React Testing Library)