Align Electron drag headers and sidebar branding spacing

- Update `ChatView` so Electron uses a fixed 52px drag titlebar, including empty-thread state.
- Make `DiffPanel` header use the same Electron drag-region sizing.
- Consolidate Sidebar drag-region into branding row and remove separate spacer div.
- Co-authored-by: codex <codex@users.noreply.github.com>
86e7bd000cJulius Marminge committed on 2/12/2026, 11:43:05 PMparent1cad53d
3 files changedLine totals unavailable