033: fix preview_translation route + MultiSelect label regression

1. preview_translation route: missing await on async preview_rows()
   - preview_rows() is async def, called without await
   - returned coroutine object instead of result -> 'coroutine not iterable' error

2. MultiSelect.svelte: opt.label -> opt.name
   - option type is {code, name} but template used {opt.label}
   - rendered empty spans instead of language names

frontend/src/lib/components/ui/MultiSelect.svelte

@@ -89,7 +89,7 @@
             onchange={() => toggle(opt.code)}
             class="rounded border-border-strong text-primary focus-visible:ring-primary-ring"
           >
-          <span>{opt.label}</span>
+          <span>{opt.name}</span>
         </div>
       {/each}
     {/if}