Fix retired option verification with noisy WP-CLI output

[chubes4]

Summary

• probe retired Homeboy option absence through wp eval exit status instead of parsing wp option list output
• use an identity-safe sentinel so every persisted option value remains distinguishable from absence
• retain fail-closed behavior when WordPress cannot verify state
• cover diagnostic text emitted on stdout

Verification

• bash tests/integration-adapters.sh
• bash -n lib/integration-adapters.sh tests/integration-adapters.sh
• live PHP 8.5/WP-CLI probe returned success while deprecation diagnostics were emitted

Closes #563.

AI assistance

OpenAI GPT-5.6 Sol via OpenCode diagnosed the live upgrade failure, implemented and verified the focused repair, and orchestrated the tracked worktree, commit, and PR submission.