fix access priorities of each level in LeveledOptions (#1118)

[MitchLewis930]

PR_056

---

Note

Low Risk
Small change to configuration option lookup order plus a targeted test; low risk but could affect how conflicting config values are resolved.

Overview
Fixes option resolution in LeveledOptions#[] so lookups prefer the most recently shifted/loaded option level (iterates @set in reverse), ensuring later config layers override earlier ones.

Adds a regression test verifying workers set via the DSL can be mutated/overwritten after load without being masked by earlier option layers.

^{Written by Cursor Bugbot for commit 8509829. This will update automatically on new commits. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with Cloud Agents, enable Autofix in the Cursor dashboard.}

[cursor]

flatten method uses inconsistent priority after [] change

Medium Severity

The [] method now uses reverse_each to give later levels higher priority (last wins), but the flatten method still uses forward @set.each with ||=, which gives earlier levels higher priority (first wins). This causes options[:key] and options.flatten[:key] to return different values when the same key exists in multiple levels, breaking consistency when flatten! is called.