feat(server): persist activity history on the server and expose it to the dashboard UI via /api/activity instead of relying on fragile localStorage

update_main.patch

@@ -0,0 +1,25 @@
+--- server/src/main.rs
++++ server/src/main.rs
+@@ -225,6 +225,20 @@
+         next_id: AtomicUsize::new(1),
+     });
+ 
++    let app_state_clone = Arc::clone(&app_state);
++    let mut rx = state.activity_tx.subscribe();
++    tokio::spawn(async move {
++        while let Ok(msg) = rx.recv().await {
++            let senders: Vec<_> = app_state_clone
++                .clients
++                .read()
++                .unwrap_or_else(|e| e.into_inner())
++                .values()
++                .cloned()
++                .collect();
++            for client_tx in senders {
++                let _ = client_tx.try_send(msg.clone());
++            }
++        }
++    });
++
+     let app = Router::new()
+             .route(