Fix agent push for unsupported workflow nodes

[kraenhansen]

Summary

• Bypass generated SDK workflow-node union validation when pushing workflows containing the SDK-missing say node type
• Send affected agent create/update requests through the SDK fetcher with the same normalized request body
• Add regression coverage for creating and updating workflows containing say nodes

Testing

• pnpm install --frozen-lockfile && pnpm run build && pnpm jest src/__tests__/workflow.test.ts --runInBand
• pnpm run build && pnpm run test && pnpm run lint (passes; lint reports existing no-explicit-any warnings in unrelated test files)