[dplyukhin]

What was changed

• Synchronize model.wit and workflow-service.wit with the copy in temporalio/api.
• Modify the generator to use new names for Go SDK internal APIs.

Why?

Go SignalWithStart

Checklist

1. Closes: N/A
2. How was this tested:
   • Full cargo validate passed with the configured mise tools and Go 1.26.0.
   • Focused Go and TypeScript generation tests passed.
   • TypeScript type checking and workflow-service runtime tests passed, including encoded-header passthrough.
   • Compared the WIT copies: the shared model is byte-identical; service differences are limited to the standalone integration settings listed above.
3. Any docs updates needed?
   • Added a changelog fragment. No public CLI changes.

Related changes

• Canonical API WIT annotations: Add Go annotations to model.wit and workflow-service.wit api#894
• SDK registry prerequisite: Add system nexus operation registry sdk-go#2721

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