Define and Document Application UI Build/Serve Contract for Workflow Engine

[intel352]

Document and enforce a standardized process for building and serving workflow application UIs using static.fileserver.

Tasks

• Standardize UI build output location for workflow apps.
• Define YAML patterns for static.fileserver usage (root, prefix, spaFallback, cacheMaxAge, dependsOn).
• Provide wfctl build-ui command for UI build automation and validation.
• Write CI and deployment steps for UI artifacts.
• Add documentation/runnable examples for development workflow (API proxy, hot-reload, serving).

Acceptance

• Workflow applications can reliably build and serve their UIs as SPAs with static.fileserver.
• Process is documented and reproducible for teams.

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Copilot Agent assigned (can be tackled in parallel).

Linked to broader UI refactor effort.