feat(ui): indicate subscribed state in subscribe button

front/src/components/channels/SubscribeButton.vue

@@ -49,9 +49,9 @@ const loginModal = ref()
 <template>
   <Button
     v-if="store.state.auth.authenticated"
-    :class="['pink', {'inverted': isSubscribed}, {'favorited': isSubscribed}]"
+    :class="['pink', {'favorited': isSubscribed}]"
     outline
-    icon="bi-heart-fill"
+    :aria-pressed="isSubscribed || undefined"
     @click.stop="toggle"
   >
     {{ title }}