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/hooks/useCarousel.ts

@@ -3,17 +3,13 @@ import create, { UseStore } from "zustand";
 interface CarouselState {
   shouldOpen: boolean;
   showCoachMark: boolean;
-  showCopilotCarousel: boolean;
   setShouldOpen: (shouldOpen: boolean) => void;
   setShowCoachMark: (showCoachMark: boolean) => void;
-  setShowCopilotCarousel: (showCopilotCarousel: boolean) => void;
 }
 
 export const useCarousel: UseStore<CarouselState> = create((set) => ({
   shouldOpen: false,
   showCoachMark: false,
-  showCopilotCarousel: false,
   setShouldOpen: (shouldOpen: boolean) => set({ shouldOpen }),
   setShowCoachMark: (showCoachMark: boolean) => set({ showCoachMark }),
-  setShowCopilotCarousel: (showCopilotCarousel: boolean) => set({ showCopilotCarousel }),
 }));