feat(ui): conditional model selector shadow logic (#681)

* feat(ui): conditional model selector shadow logic (#678)

- Update ModelSelectorList to conditionally render shadow based on scroll state
- Update CommandList to forward ref for scroll detection
- Resolves #678

* Update components/ui/command.tsx

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* fix(ui): update listRef type to match CommandList forwarded ref

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

components/ui/command.tsx

@@ -77,12 +77,13 @@ function CommandInput({
   )
 }
 
-function CommandList({
-  className,
-  ...props
-}: React.ComponentProps<typeof CommandPrimitive.List>) {
+const CommandList = React.forwardRef<
+  React.ElementRef<typeof CommandPrimitive.List>,
+  React.ComponentPropsWithoutRef<typeof CommandPrimitive.List>
+>(({ className, ...props }, ref) => {
   return (
     <CommandPrimitive.List
+      ref={ref}
       data-slot="command-list"
       className={cn(
         "max-h-[300px] scroll-py-1 overflow-x-hidden overflow-y-auto",
@@ -91,7 +92,8 @@ function CommandList({
       {...props}
     />
   )
-}
+})
+CommandList.displayName = CommandPrimitive.List.displayName ?? "CommandList"
 
 function CommandEmpty({
   ...props