Describe the bug

The SidebarSeparator component causes overflow issues when used with horizontal orientation.
The component currently uses w-auto which conflicts with the underlying Separator component's
default styling, leading to unwanted horizontal overflow.

Affected Components

• SidebarSeparator (all styles: default, new-york, new-york-v4)

Root Cause

The SidebarSeparator component applies w-auto unconditionally, but this conflicts with the
Separator component's base classes which set different width behaviors based on orientation.
The w-auto override should only apply to horizontal separators to prevent overflow issues.

Current Implementation

<Separator
  data-sidebar="separator"
  :class="cn('mx-2 w-auto bg-sidebar-border', props.class)"
>

Expected Behavior

The separator should not cause horizontal overflow and should respect the orientation-specific
width styling.

Proposed Solution

Change w-auto to data-[orientation=horizontal]:w-auto to make the width override more
specific and only apply to horizontal separators:

<Separator
  data-sidebar="separator"
  :class="cn('mx-2 data-[orientation=horizontal]:w-auto bg-sidebar-border', props.class)"
>

Additional Context

This issue is related to the same problem in the main shadcn-ui/ui library:
shadcn-ui/ui#8498

Screenshots