Sort chat recents by last activity (#6844)

* show chat by by last activity

* Update chat thread updated_at logic and enhance sidebar chat item handling

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: Lee Jackson <130007945+Imagineer99@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

studio/frontend/src/components/app-sidebar.tsx

@@ -359,7 +359,11 @@ export function AppSidebar() {
   const activeProjectId = isChatRoute
     ? ((search.project as string | undefined) ?? null)
     : null;
-  const { items: allChatItems } = useChatSidebarItems({
+  const {
+    items: allChatItems,
+    archivedItems: archivedChatItems,
+    loaded: chatItemsLoaded,
+  } = useChatSidebarItems({
     enabled: !isStudioRoute,
     requireMessages: false,
   });
@@ -1306,6 +1310,16 @@ export function AppSidebar() {
                       renderChatSidebarItem(item, "recent"),
                     )}
                   </SidebarMenu>
+                  {/* "No chats yet" only when there is truly no history:
+                      project-scoped and archived threads leave Recents empty
+                      but still count as existing chats. */}
+                  {chatItemsLoaded &&
+                    allChatItems.length === 0 &&
+                    archivedChatItems.length === 0 && (
+                      <p className="px-3 py-2 text-xs text-muted-foreground">
+                        {t("shell.navigation.noChatsYet")}
+                      </p>
+                    )}
                 </SidebarGroupContent>
               </CollapsibleContent>
             </SidebarGroup>