[codex] Refresh trunk before sync restack

[mark-pro]

Summary

Refresh sync so it updates the configured trunk branch before the existing repair, cleanup, and restack flow continues.

What Changed

• add a sync preflight trunk refresh step that captures the original branch, switches to trunk, and runs git pull --rebase
• abort trunk-refresh rebase state and restore the starting branch if that preflight fails
• add a dedicated RefreshingTrunk sync status and render coverage
• expand sync smoke tests for trunk refresh success, preflight failure cleanup, and existing remote cleanup / PR repair flows

Why

sync was restacking against stale local trunk state, which meant remote trunk updates were not consistently reflected before the normal restack plan ran.

Validation

• rustup run stable cargo fmt --all
• cargo check
• cargo test