Add test coverage for critical automation scripts

[PAMulligan]

Summary

Only 2 of 25+ scripts have automated tests (canva-pipeline.test.js, visual-diff.test.js). Critical pipeline infrastructure scripts have zero test coverage.

Scripts Needing Tests (Priority Order)

P0 — Pipeline Infrastructure

• pipeline-cache.js — cache validity, invalidation, status reporting
• stage-profiler.js — timing data, report generation, history tracking
• metrics-dashboard.js — HTML generation, summary output, trend analysis
• incremental-build.sh — phase detection, cache hits/misses, parallel execution
• sync-tokens.sh — drift detection, lockfile comparison, auto-update

P1 — Quality Gate Scripts

• verify-tokens.sh — hardcoded value detection, token violation reporting
• verify-test-coverage.sh — component-to-test mapping validation
• check-dead-code.sh — unused export detection, false positive handling
• check-security.sh — vulnerability scanning, severity filtering

P2 — Generation Scripts

• generate-stories.sh — Storybook story output validation
• generate-component-docs.sh — MDX output validation
• generate-api-client.sh — OpenAPI spec parsing, TypeScript output

P3 — Verification Scripts

• check-responsive.sh — breakpoint screenshot capture
• audit-cross-browser-css.sh — CSS compatibility detection
• regression-test.sh — baseline comparison, threshold handling

Acceptance Criteria

• Each script has at least one test file in scripts/__tests__/
• Tests cover happy path and primary error cases
• Tests can run without external dependencies (MCP servers, browsers) where possible
• CI can run the test suite