style(desktop): shrink button scale, flush overlay sidebar, variant-ize stray buttons

- Buttons: smaller default font (14px -> 13px) and tighter padding-driven sizes
  across every variant; the chunky shadcn scale read as oversized in a dense
  desktop UI.
- Overlay split layout (settings / command center): the shared OverlayView top
  padding left the card surface showing as a gap above the sidebar. Move the
  titlebar clearance into each column so the sidebar background runs flush to
  the card's top edge.
- Consolidate buttons that hardcoded size/radius/font onto the proper size
  variants (tooltip-icon-button, overlay close, cron IconAction, SidebarTrigger,
  gateway system button, session-row actions radius, title chip radius, release
  notes link) so styling flows from variant props, not per-call overrides.
  Composer and the inline approval strip are intentionally left as-is.

apps/desktop/src/components/assistant-ui/tooltip-icon-button.tsx

@@ -14,11 +14,11 @@ export const TooltipIconButton = forwardRef<HTMLButtonElement, TooltipIconButton
   ({ children, tooltip, side: _side = 'bottom', className, ...rest }, ref) => {
     return (
       <Button
-        size="icon"
+        size="icon-xs"
         variant="ghost"
         {...rest}
         aria-label={tooltip}
-        className={cn('aui-button-icon size-6 p-1', className)}
+        className={cn('aui-button-icon', className)}
         ref={ref}
         title={tooltip}
       >

apps/desktop/src/components/ui/button.tsx

@@ -8,7 +8,7 @@ import { cn } from '@/lib/utils'
 // fixed heights — so they stay snug and scale with content. Only icon buttons
 // (inherently square) carry the shared 4px radius.
 const buttonVariants = cva(
-  "inline-flex shrink-0 cursor-pointer items-center justify-center gap-2 rounded-none text-sm font-medium whitespace-nowrap transition-all outline-none focus-visible:border-ring focus-visible:ring-[0.1875rem] focus-visible:ring-ring/50 disabled:pointer-events-none disabled:cursor-default disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-destructive/20 dark:aria-invalid:ring-destructive/40 [&_svg]:pointer-events-none [&_svg]:shrink-0 [&_svg:not([class*='size-'])]:size-4",
+  "inline-flex shrink-0 cursor-pointer items-center justify-center gap-1.5 rounded-none text-[0.8125rem] leading-5 font-medium whitespace-nowrap transition-all outline-none focus-visible:border-ring focus-visible:ring-[0.1875rem] focus-visible:ring-ring/50 disabled:pointer-events-none disabled:cursor-default disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-destructive/20 dark:aria-invalid:ring-destructive/40 [&_svg]:pointer-events-none [&_svg]:shrink-0 [&_svg:not([class*='size-'])]:size-3.5",
   {
     variants: {
       variant: {
@@ -22,10 +22,10 @@ const buttonVariants = cva(
         link: 'text-primary underline-offset-4 decoration-current/20 hover:underline'
       },
       size: {
-        default: 'px-3.5 py-1.5 has-[>svg]:px-3',
-        xs: "gap-1 px-2 py-1 text-xs has-[>svg]:px-1.5 [&_svg:not([class*='size-'])]:size-3",
-        sm: 'gap-1.5 px-3 py-1 has-[>svg]:px-2.5',
-        lg: 'px-6 py-2.5 has-[>svg]:px-4',
+        default: 'px-3 py-1 has-[>svg]:px-2.5',
+        xs: "gap-1 px-2 py-0.5 text-[0.6875rem] leading-4 has-[>svg]:px-1.5 [&_svg:not([class*='size-'])]:size-3",
+        sm: 'px-2.5 py-0.5 has-[>svg]:px-2',
+        lg: 'px-5 py-2 text-sm leading-5 has-[>svg]:px-4',
         icon: 'size-9 rounded-[4px]',
         'icon-xs': "size-6 rounded-[4px] [&_svg:not([class*='size-'])]:size-3",
         'icon-sm': 'size-8 rounded-[4px]',

apps/desktop/src/components/ui/sidebar.tsx

@@ -242,14 +242,14 @@ function SidebarTrigger({ className, onClick, ...props }: React.ComponentProps<t
 
   return (
     <Button
-      className={cn('size-7', className)}
+      className={className}
       data-sidebar="trigger"
       data-slot="sidebar-trigger"
       onClick={event => {
         onClick?.(event)
         toggleSidebar()
       }}
-      size="icon"
+      size="icon-sm"
       variant="ghost"
       {...props}
     >