Align diff panel surfaces with app theme colors

- add diff-specific wrapper classes in `DiffPanel` for targeted theming
- override diff renderer color variables to match card/background palette
- soften chat markdown Shiki code-block background for consistency
fcbb494af7Julius Marminge committed on 2/28/2026, 11:17:03 PM· committed by Julius Marmingeparent2980a85
2 files changedLine totals unavailable