chore: Add "Coming Soon" overlay to voice channel selector (#11835)

# Pull Request Template

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<img width="867" alt="image"
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---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/javascript/dashboard/components/widgets/ChannelItem.vue

@@ -57,6 +57,12 @@ export default {
         'voice',
       ].includes(key);
     },
+    isComingSoon() {
+      const { key } = this.channel;
+      // Show "Coming Soon" only if the channel is marked as coming soon
+      // and the corresponding feature flag is not enabled yet.
+      return ['voice'].includes(key) && !this.isActive;
+    },
   },
   methods: {
     getChannelThumbnail() {
@@ -79,6 +85,7 @@ export default {
     :class="{ inactive: !isActive }"
     :title="channel.name"
     :src="getChannelThumbnail()"
+    :is-coming-soon="isComingSoon"
     @click="onItemClick"
   />
 </template>