Persist GitHub CLI account selection

[PabloZaiden]

Summary

• add --gh-user/--gh-host to pin GH_TOKEN injection to a specific gh account
• persist githubAuth metadata in .devbox/state.json and expose it in status
• document the account selection precedence for downstream tools

Validation

• bun run build
• bun run test:fast

[Copilot]

Pull request overview

This PR adds the ability to pin GH_TOKEN injection to a specific GitHub CLI (gh) account by introducing --gh-user/--gh-host, persisting the selected account metadata in .devbox/state.json, surfacing it in devbox status, and documenting the selection precedence.

Changes:

• Add --gh-user / --gh-host parsing for up and rebuild, and persist the chosen { host, user } as githubAuth in workspace state.
• Thread the persisted githubAuth preference through host environment resolution so gh auth token can target a specific account.
• Extend status output, tests, and README docs to include/describe githubAuth.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/status.test.ts	Updates status expectations to include githubAuth.
tests/runtime.test.ts	Adds unit tests for buildGhCliTokenArgs.
tests/core.test.ts	Adds coverage for arg parsing validation and persisted githubAuth loading.
tests/arise.test.ts	Updates workspace state fixtures to include githubAuth.
src/status.ts	Adds githubAuth to DevboxStatus and returns it from state.
src/runtime.ts	Adds GithubAuthPreference plumbing + buildGhCliTokenArgs for targeted gh auth token.
src/core.ts	Extends workspace state schema/migration to include githubAuth; adds CLI flag parsing.
src/cli.ts	Resolves githubAuth preference from flags/env/state and persists it after up/rebuild.
README.md	Documents flags, precedence, and status payload example including githubAuth.

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