Prompt for workspace during OAuth login

[Mukil Loganathan (langchain-infra)]

Summary

• list available workspaces after langsmith login completes OAuth and prompt for a default workspace in interactive terminals
• allow non-interactive login to complete without a workspace, but print a warning with --workspace-id / workspace set-default guidance
• format LangSmith JSON error responses so workspace-required auth errors show the server error code and message

Commands and observed output

• langsmith login --api-url https://api.smith.langchain.com --no-browser --timeout 10m
  • opened https://smith.langchain.com/activate and displayed a device code
  • after authorization, printed Select a default workspace: with numbered workspace options
  • selecting 1 saved workspace_id: ebbaf2eb-769b-4505-aca2-d11de10372a4 for LangChain Inc
• langsmith project list --limit 1 using the saved temp profile returned a project from the selected workspace
• langsmith workspace list --format pretty using the saved temp profile returned the workspace table

Tests

• go test ./internal/cmd -run TestLogin -count=1
• go test ./internal/client -run TestRawGet_JSONHTTPErrorIncludesMessage -count=1
• go test ./... -count=1