fix: TRAC-513 - clear stale variation override on stencil pull

[parthshahp]

Summary

• stencil pull was failing to clear a previously-stored variation value when the corresponding Page Builder field was emptied — the stale value persisted locally even after re-pulling.
• Root cause: mergeThemeConfiguration compared each remote setting only against the top-level default in config.json. When a Page Builder field was cleared, the remote variation value matched the default, so the loop thought "in sync" and never overwrote the stale variation.settings[key].
• Fix: compare the remote value against the effective local value — the variation override if one exists, otherwise the default — so stale overrides get cleared back to the default.

Linear: LTRAC-528 · Jira: TRAC-513

Testing

Screen.Recording.2026-05-14.at.10.34.58.AM.mov