We are polishing the DevIndex UI layout.
The Grid and Controls containers need consistent styling with the Header Toolbar.

Scope:

• Apply --devindex-header-shadow to GridContainer.
• Apply --devindex-header-shadow to ControlsContainer.
• Add border-radius (top-left, bottom-left) to ControlsContainer to match the grid.
• Ensure ControlsContainer border color matches the grid border color.