Remove redundant checkbox-input class from TreeCheckbox

The selection slot div in TreeCheckbox was using both className="checkbox-input"
and data-slot="selection", causing duplicate styling. The CSS already has
comprehensive [data-slot="selection"] rules that cover all the necessary
styling, making the checkbox-input class redundant and confusing.

Changes:
- Removed className="checkbox-input" from TreeCheckbox selection slot
- CSS [data-slot="selection"] rules already include all necessary styling
- Updated 5 test snapshots to reflect the cleaner markup

This addresses the Copilot review comment about duplicate/conflicting
styling between .checkbox-input class and [data-slot="selection"] attribute.

revert lock files

Author: OpenStaxClaude

src/components/Tree/TreeCheckbox.tsx

@@ -66,7 +66,7 @@ export const TreeCheckbox = ({
       style={checkboxStyle}
       isDisabled={isDisabled}
     >
-      <div className="checkbox-input" data-slot="selection" />
+      <div data-slot="selection" />
       {children}
     </RACCheckbox>
   );

src/components/Tree/__snapshots__/TreeCheckbox.spec.tsx.snap

@@ -74,7 +74,6 @@ exports[`TreeCheckbox handles disabled state 1`] = `
     />
   </span>
   <div
-    className="checkbox-input"
     data-slot="selection"
   />
   Click Me
@@ -156,7 +155,6 @@ exports[`TreeCheckbox handles indeterminate state 1`] = `
     />
   </span>
   <div
-    className="checkbox-input"
     data-slot="selection"
   />
   Click Me
@@ -237,7 +235,6 @@ exports[`TreeCheckbox handles options 1`] = `
     />
   </span>
   <div
-    className="checkbox-input"
     data-slot="selection"
   />
   Click Me
@@ -318,7 +315,6 @@ exports[`TreeCheckbox matches snapshot 1`] = `
     />
   </span>
   <div
-    className="checkbox-input"
     data-slot="selection"
   />
   Click Me
@@ -400,7 +396,6 @@ exports[`TreeCheckbox supports slot="selection" 1`] = `
     />
   </span>
   <div
-    className="checkbox-input"
     data-slot="selection"
   />
   Click Me