Ignore transactional install state

[yazanabuashour]

Summary

• ignore transactional candidate directories, recovery journals, and promotion locks
• prevent normal local builds from dirtying the checkout

Follow-up to #834.

Validation

• git diff --check
• verified all three paths with git check-ignore

Checklist

• This pull request is ready for review and is no longer a draft.
• I followed CONTRIBUTING.md, kept the change focused, edited source files rather than generated output, and removed unrelated changes.
• If this fixes upstream drift, it targets only the latest CODEX.DMG and removes obsolete fallback code and tests from the affected area.
• I added or updated relevant tests, ran the validation listed above, and confirmed that required CI checks pass.
• I reviewed the final diff with my coding agent using maximum reasoning effort, addressed all findings, and reran the relevant tests.

[ilysenko]

Reviewed the current head. The ignore rules are narrowly scoped to generated transactional install state, match the documented runtime paths, and all required checks pass.