make widgets wider in classic view

the style of widgets was changed by @Insert5StarName (@Marie?) with
commit e14fd331 as part of !178

I'm not sure if it was intentional or accidental, and I'm also not
sure why nobody noticed before 2024.11 (maybe something else kept the
widgets wider?)

Anyway, this change seems to be enough

packages/frontend/src/ui/classic.vue

@@ -260,6 +260,7 @@ onMounted(() => {
 			position: sticky;
 			top: 0;
 			height: 100%;
+			width: 300px;
 			padding-top: 16px;
 			box-sizing: border-box;
 			overflow: auto;