Refactor image grid empty state, enhance header styles, and update ChannelRef struct

- Changed the empty state message in ImageGrid to use a dedicated class for styling.
- Adjusted padding and border-radius for the "Guild Watcher" label in the header for better aesthetics.
- Introduced a new class for the status indicator dot and linked its visibility to the connection state.
- Updated ChannelRef struct to include optional fields for thread_id and thread_name with appropriate serialization settings.

services/frontend/shared-types/src/message.rs

@@ -131,12 +131,16 @@ impl<'de> Deserialize<'de> for EmbedMedia {
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[serde(rename_all = "camelCase")]
 pub struct ChannelRef {
     pub channel_id: String,
+    #[serde(default)]
     #[serde(skip_serializing_if = "Option::is_none")]
     pub channel_name: Option<String>,
+    #[serde(default)]
     #[serde(skip_serializing_if = "Option::is_none")]
     pub thread_id: Option<String>,
+    #[serde(default)]
     #[serde(skip_serializing_if = "Option::is_none")]
     pub thread_name: Option<String>,
 }