Studio: reorder sidebar, rename Hub to Models (#7327)

* Studio: put Hub above Projects in the sidebar

Swap the two nav rows so Hub sits directly under New Chat, ahead of
Projects. Order only, no behavior change.

* Studio: rename Hub to Models, lowercase New chat

Rename the Hub nav row and its page heading to Models (localized in all
locales). Use sentence case 'New chat' in the English label.

* Studio: fix dataset title and stale Hub tab hints after rename

Show 'Datasets' as the catalog heading in dataset mode, not 'Models'.
Update the download-conflict toasts to point at the Models tab.

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

@@ -1357,6 +1357,18 @@ export function AppSidebar() {
         <SidebarGroup className="group-data-[collapsible=icon]:px-0 pl-1.5 pr-2 py-0 shrink-0">
           <SidebarGroupContent>
             <SidebarMenu>
+              <NavItem
+                icon={DashboardCircleIcon}
+                label={t("shell.navigation.hub")}
+                active={pathname === "/hub" || pathname.startsWith("/hub/")}
+                onClick={() => {
+                  navigate({ to: "/hub" });
+                  closeMobileIfOpen();
+                }}
+                onIntent={() => {
+                  preloadSilently(router.preloadRoute({ to: "/hub" }));
+                }}
+              />
               <NavItem
                 icon={Folder01Icon}
                 label="Projects"
@@ -1392,18 +1404,6 @@ export function AppSidebar() {
                   </span>
                 </button>
               </NavItem>
-              <NavItem
-                icon={DashboardCircleIcon}
-                label={t("shell.navigation.hub")}
-                active={pathname === "/hub" || pathname.startsWith("/hub/")}
-                onClick={() => {
-                  navigate({ to: "/hub" });
-                  closeMobileIfOpen();
-                }}
-                onIntent={() => {
-                  preloadSilently(router.preloadRoute({ to: "/hub" }));
-                }}
-              />
               {/* Train has a labelled section when expanded; plain icon here only when collapsed. */}
               <NavItem
                 icon={TestTubeOutlineIcon}