change default unit to liter

Since the inventory is mostly containing enginge oils, which are sold per liter, the default unit for a new part is set to liter

src/routes/parts/new/+page.svelte

@@ -54,7 +54,7 @@
   <div class="row">
     <label>
       {$t('parts.unit')}
-      <input name="unit" value={values.unit ?? 'pcs'} />
+      <input name="unit" value={values.unit ?? 'liter'} />
     </label>
     <label>
       {$t('parts.reorder_level')}