chore(core): adjust tab height and windows control, remove input background (#12862)

close AF-2697, AF-2696

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Style**
- Made the AI chat input field background transparent for improved
visual consistency.
- Reduced the size of window app control buttons and removed extra
padding from the close button.
- Decreased the height of tabs and the width of the window app controls
placeholder for a more compact layout.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/core/src/modules/app-tabs-header/views/styles.css.ts

@@ -78,7 +78,7 @@ export const tabWrapper = style({
 });
 
 export const tab = style({
-  height: 32,
+  height: 26,
   minWidth: 32,
   maxWidth: tabMaxWidth,
   width: 200,
@@ -243,7 +243,7 @@ export const spacer = style({
 });
 
 export const windowsAppControlsPlaceholder = style({
-  width: '160px',
+  width: '120px',
   height: '100%',
   flexShrink: 0,
 });