feat: publish shared task and reply activities through MCP

src/features/activities/events.server.ts

@@ -0,0 +1,18 @@
+type Listener = () => void;
+const state = globalThis as typeof globalThis & { workspaceActivityListeners?: Set<Listener> };
+const listeners = (state.workspaceActivityListeners ??= new Set<Listener>());
+export function subscribeActivities(listener: Listener) {
+  listeners.add(listener);
+  return () => {
+    listeners.delete(listener);
+  };
+}
+export function notifyActivities() {
+  for (const listener of listeners) {
+    try {
+      listener();
+    } catch {
+      /* A disconnected viewer cannot fail a committed write. */
+    }
+  }
+}