Move diff theme overrides into DiffPanel unsafeCSS

- Inject diff palette overrides via `unsafeCSS` in `DiffPanel`
- Add `diff-panel-viewport` background and keep file container border/background styling in `index.css`
- Switch panel root from `bg-card` to `bg-background` for consistent surface tone
d052d481d8Julius Marminge committed on 2/28/2026, 11:17:03 PM· committed by Julius Marmingeparentfcbb494
2 files changedLine totals unavailable