fix: 投稿フォームの字数上限計算を実際の投稿内容に合わせる (#14466)

packages/frontend/src/components/MkPostForm.vue

@@ -245,7 +245,7 @@ const submitText = computed((): string => {
 });
 
 const textLength = computed((): number => {
-	return (text.value + imeText.value).trim().length;
+	return (text.value + imeText.value).length;
 });
 
 const maxTextLength = computed((): number => {