fix: Use Canvas YAML copy handler

[BenHamiltonGit]

Summary

• Route the Canvas YAML modal's Copy button through the parent-provided copy handler.
• Add coverage for using the handler and hiding the button when no handler is provided.

Why

CanvasYamlView already wires handleYamlViewCopy into CanvasYamlModal, and that handler owns the success/error toast behavior for YAML copying. The modal was bypassing it with a direct navigator.clipboard.writeText(...) call, so copy result feedback was not surfaced through the existing path.

Testing

• npx eslint src/pages/workflowv2/CanvasYamlModal.tsx src/pages/workflowv2/CanvasYamlModal.spec.tsx
• npm run test:run -- CanvasYamlModal.spec.tsx
• npx prettier --check src/pages/workflowv2/CanvasYamlModal.tsx src/pages/workflowv2/CanvasYamlModal.spec.tsx
• docker compose -f docker-compose.dev.yml exec app bash -lc "cd web_src && npm run build"

[superplanehq-integration]

👋 Commands for maintainers:

• /sp start - Start an ephemeral machine (takes ~30s)
• /sp stop - Stop a running machine (auto-executed on pr close)

[BenHamiltonGit]

Thanks for taking a look. I originally found SuperPlane through a Product Engineer listing and opened this PR as the requested proof-of-work step.

I noticed this now conflicts with #5025, which removes CanvasYamlModal.tsx as part of the new Files tab work, so this specific fix may be superseded by that UI change. Either way, I enjoyed digging into the flow and would still be interested in future product engineering opportunities with the team.

Portfolio: https://portfolio-2rbk.onrender.com/