Perf/copilot cleanup and optimizations (#2447)

* perf: remove deprecated copilot feature, add ARM timeouts, fix race conditions

- Remove entire QueryCopilot feature (~50 files deleted, ~30 files cleaned)
- Remove CopilotConfigured and SampleDataLoaded metric phases
- Fix DatabaseTreeRendered 76% stuck rate (remove one-shot guard in useMetricPhases)
- Add 8s default timeout to ARM requests (AbortController-based)
- Fix MSAL token forceRefresh (true -> false, use cache)
- Add concurrency limit of 5 to collection loading in Explorer
- Remove orphaned SampleDataClient.ts and queryCopilotSampleData.json
- Clean up dead sampleDataConnectionInfo field from UserContext

* Clean up copilot and optimize initialization

* Clean up copilot and optimize initialization

src/Main.tsx

@@ -25,7 +25,6 @@ import "../externals/jquery.typeahead.min.css";
 import "../externals/jquery.typeahead.min.js";
 // Image Dependencies
 import { SidePanel } from "Explorer/Panes/PanelContainerComponent";
-import { QueryCopilotCarousel } from "Explorer/QueryCopilot/CopilotCarousel";
 import { SidebarContainer } from "Explorer/Sidebar";
 import { KeyboardShortcutRoot } from "KeyboardShortcuts";
 import "allotment/dist/style.css";
@@ -173,7 +172,6 @@ const App = (): JSX.Element => {
 
 const DivExplorer: React.FC<{ explorer: Explorer }> = ({ explorer }) => {
   const isCarouselOpen = useCarousel((state) => state.shouldOpen);
-  const isCopilotCarouselOpen = useCarousel((state) => state.showCopilotCarousel);
 
   return (
     <div
@@ -220,7 +218,6 @@ const DivExplorer: React.FC<{ explorer: Explorer }> = ({ explorer }) => {
       {<QuickstartCarousel isOpen={isCarouselOpen} />}
       {<SQLQuickstartTutorial />}
       {<MongoQuickstartTutorial />}
-      {<QueryCopilotCarousel isOpen={isCopilotCarouselOpen} explorer={explorer} />}
     </div>
   );
 };