AD-1102: Add workflow routes

[alph-cmky]

Summary

• Add workflow route handlers for create, list, get, update, and delete operations.
• Map workflow validation failures to 400 responses without persisting invalid workflows.
• Map missing workflows to 404 responses.
• Keep route handlers thin by delegating persistence and validation to workflow-service.
• Export workflow route APIs from the server package and update the AD-1102 backlog checklist.

Testing

• TDD red check: pnpm test apps/server/src/workflows/workflow-routes.test.ts initially failed because workflow-routes.js did not exist.
• pnpm test apps/server/src/workflows/workflow-routes.test.ts
• pnpm lint && pnpm format && pnpm typecheck && pnpm test && pnpm build

Stacked on #51.