fix: keep artifact cleanup branch identity stable

[chubes4]

Summary

• Resolve artifact cleanup branch identity from each worktree HEAD in both dry-run and apply-plan revalidation paths.
• Extend the bounded artifact cleanup smoke test to cover slashed branches where the directory slug differs from the real branch.

Fixes #427.

Testing

• php tests/smoke-worktree-cleanup-artifacts-bounded.php
• homeboy lint --changed-since origin/main
• homeboy test --changed-since origin/main

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Diagnosed the cleanup branch mismatch, drafted the code/test changes, and ran local verification; Chris directed the issue and remains responsible for review/merge.

[homeboy-ci]

Homeboy Results — data-machine-code

Lint

✅ lint — passed

ℹ️ Full options: homeboy docs commands/lint
ℹ️ Save lint baseline: homeboy lint data-machine-code --baseline
Deep dive: homeboy lint data-machine-code --changed-since 488ac1e

Test

✅ test — passed

ℹ️ Auto-fix lint issues: homeboy refactor data-machine-code --from lint --write
ℹ️ Collect coverage: homeboy test data-machine-code --coverage
ℹ️ Pass args to test runner: homeboy test -- [args]
ℹ️ Full options: homeboy docs commands/test
Deep dive: homeboy test data-machine-code --changed-since 488ac1e

Audit

✅ audit — passed

• dead_code — 5 finding(s)
• intra-method-duplication — 1 finding(s)
• test_coverage — 1 finding(s)
• Total: 7 finding(s)

Deep dive: homeboy audit data-machine-code --changed-since 488ac1e

Tooling versions

• Homeboy CLI: homeboy 0.182.0+2923d3d
• Extension: wordpress from https://github.com/Extra-Chill/homeboy-extensions
• Extension revision: 65942142
• Action: unknown@unknown