feat: implement unread notification count and enhance user listing with pagination

crates/domain/src/models/thought.rs

@@ -25,6 +25,17 @@ pub struct Thought {
     pub updated_at: Option<DateTime<Utc>>,
 }
 
+impl Visibility {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            Visibility::Public => "public",
+            Visibility::Followers => "followers",
+            Visibility::Unlisted => "unlisted",
+            Visibility::Direct => "direct",
+        }
+    }
+}
+
 impl Thought {
     pub fn new_local(
         id: ThoughtId,