feat(workflow-studio): Zapier-inspired local automation graph

Summary

Adds src/workflow-studio/ — trigger/action/filter runner. No LIVE OAuth connectors. Amplify/README + icons.

DOCUMENTED vs LIVE

See src/workflow-studio/README.md — honest comparison; no fabricated LIVE access.

Test plan

• cd src/workflow-studio && npm ci && npm test && npm run build (4 tests)
• Smoke the UI