feat(ap): @mention notification from inbound remote Notes

crates/adapters/activitypub/src/note.rs

@@ -24,6 +24,8 @@ pub struct ThoughtNote {
     pub sensitive: bool,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub summary: Option<String>,
+    #[serde(skip_serializing_if = "Vec::is_empty", default)]
+    pub tag: Vec<serde_json::Value>,
 }
 
 impl ThoughtNote {
@@ -50,6 +52,7 @@ impl ThoughtNote {
             in_reply_to,
             sensitive,
             summary,
+            tag: Vec::new(),
         }
     }
 }