Refactors header grid layout with CSS subgrid

Updates header and viewport components to use CSS subgrid for more flexible layout

Improves grid structure by:
- Replacing fixed grid columns with subgrid
- Adjusting scrollbar and overflow properties
- Simplifying header and track element positioning

src/v2/core/HeaderDrawerManager.ts

@@ -1,7 +1,7 @@
 export class HeaderDrawerManager {
   private drawer!: HTMLElement;
   private expanded = false;
-  private readonly expandedHeight = 24;
+  private readonly expandedHeight = 25;
   private readonly duration = 200;
 
   init(container: HTMLElement): void {