feat(ts-sdk): add workspace lookup and ensure helpers

[noodleonthecape]

Summary

• add TypeScript SDK RelayCast.lookupWorkspace() and RelayCast.ensureWorkspace() helpers
• add the server workspace-by-name lookup route required by the SDK flow
• expose the shared workspace lookup type/schema and document the SDK usage

cc @willwashburn

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[noodleonthecape]

cc @willwashburn

[github-actions]

Preview deployed!

Environment	URL
API	https://pr98-api.relaycast.dev
Health	https://pr98-api.relaycast.dev/health
Observer	https://pr98-observer.relaycast.dev/observer

This preview shares the staging database and will be cleaned up when the PR is merged or closed.

Run E2E tests

npm run e2e -- https://pr98-api.relaycast.dev --ci

Open observer dashboard

https://pr98-observer.relaycast.dev/observer

[willwashburn]

why can't we just use the schema.parse instead of all the manual shape checking use on lines 172-208? there has to be a more elegant way

[noodleonthecape]

Swapped the manual envelope/data shape checks over to ApiResponseSchema(WorkspaceLookupSchema).safeParse(...) and used the parsed discriminated union to handle success vs error. I also applied the same cleanup to createWorkspace for consistency since it had the same open-coded response parsing pattern. Behavior stays the same, including returning null on 404 from lookupWorkspace.