feat(ui,docs): the open tab lives in the conversation url, admin screenshots in the readme

ui/src/lib/panel/conversation-view.svelte

@@ -18,6 +18,7 @@
     onOpen,
     showTitle = true,
     initialView = "chat",
+    onViewChange,
   }: {
     client: ApiClient;
     id: string;
@@ -27,6 +28,8 @@
     showTitle?: boolean;
     // "activity" beside a deep chat's own note: the file is the thread.
     initialView?: string;
+    // The page keeps the open tab in the URL so it survives a reload.
+    onViewChange?: (view: string) => void;
   } = $props();
 
   const host = usePanelHost();
@@ -50,6 +53,10 @@
     historyKey += 1;
   }
 
+  $effect(() => {
+    onViewChange?.(view);
+  });
+
   $effect(() => {
     const { running } = feed.model;
     if (!running) {