client: always forbid MFM overflow

Some MFM overlays UI components. This should remove any possibility that
rendered MFM escapes a Note's body.

Changelog: Changed

packages/client/src/components/global/misskey-flavored-markdown.vue

@@ -175,6 +175,7 @@ withDefaults(defineProps<{
 <style lang="scss" scoped>
 .havbbuyv {
 	white-space: pre-wrap;
+	overflow: hidden;
 
 	&.nowrap {
 		white-space: pre;

packages/client/src/components/mfm.ts

@@ -334,6 +334,6 @@ export default defineComponent({
 		}).flat();
 
 		// Parse ast to DOM
-		return h('span', genEl(ast));
+		return h('div', genEl(ast));
 	},
 });