Fix stale continue-rebase confirmation after external completion

[SergioChan]

Summary

• dismiss the "All merge conflicts resolved. Continue the rebase?" confirmation when the rebase/merge has already finished externally
• only auto-close confirmations that match the localized ConflictsResolved prompt template
• add a helper test that verifies localized template matching behavior

Repro

Fixes #5197.

1. Start a rebase that produces conflicts
2. Resolve conflicts outside lazygit and trigger the continue prompt
3. Run git rebase --continue in another terminal before confirming in lazygit
4. Refresh lazygit

Before: the continue prompt could remain visible after rebase completion.
After: stale continue prompt is dismissed once no merge/rebase is in progress.

Validation

• go test ./pkg/gui/controllers/helpers -run TestMatchesPromptTemplate
• git diff --check