Rename sandbox setup to create and add sandbox update

[mxriverlynn]

Summary

• Renames skillwalker sandbox setup to skillwalker sandbox create. The old spelling now fails with Unknown argument. The hint strings in @testdouble/sandbox-integration and the docs name the new command.
• Adds skillwalker sandbox update. It deletes the Test Sandbox and recreates it from the latest Claude Code sandbox template.

How sandbox update gets the latest template

sbx has no pull command, and sbx run reuses whatever template image it already has cached. The new updateSandbox(repoRoot) works in three steps:

1. Runs sbx rm --force claude-skills-skillwalker, if the sandbox exists.
2. Runs sbx template ls and removes every docker/sandbox-templates image whose tag starts with claude-code, using sbx template rm <image id>.
3. Calls createSandbox, so sbx run fetches the current template and runs the OAuth login again.

sbx template ls can list one image under several IDs, and removing the first ID removes them all. A later rm that reports no template image therefore counts as already removed. Any other failure stops the command with a SkillwalkerError.

Notes for review

• The make sandbox-setup target keeps its name, to match the earlier consolidation decision. It now calls sandbox create.
• Running it would have deleted the local sandbox, so sandbox update has not been run against real sbx. It is covered by unit tests with a mocked Bun.spawn. The sbx template ls column layout was checked against sbx v0.29.0.

Test plan

• make test (77 files, 1016 tests passing)
• bun packages/cli/index.ts sandbox lists create, update, clean, shell
• Run ./build/skillwalker sandbox update against a real sandbox and confirm a fresh template is pulled

🤖 Generated with Claude Code