Keep diff panel mounted and reuse worker pool across layouts

- Keep the diff viewer alive when hidden to avoid remount churn
- Share diff worker pool setup via a dedicated provider
- Add `keepMounted` support to `SheetPopup` for sheet-mode persistence
f748aa88bdJulius Marminge committed on 2/19/2026, 12:45:59 AMparentba46a1b
3 files changedLine totals unavailable