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/Metrics/useMetricPhases.ts

@@ -42,19 +42,18 @@ export function useInteractive(scenario: MetricScenario, enabled = true) {
 /**
  * Hook to manage DatabaseLoad scenario phase completions.
  * Tracks tree rendering and completes Interactive phase.
- * Only completes DatabaseTreeRendered if the database fetch was successful.
+ * Only attempts to complete DatabaseTreeRendered if the database fetch was successful.
  * Note: Scenario must be started before databases are fetched (in refreshExplorer).
  *
- * Calls scenarioMonitor directly (not via React context) for the same stability reason
- * as useInteractive — avoids effect re-runs from unstable context function references.
+ * No one-shot guard is needed — completePhase is idempotent (ScenarioMonitor returns
+ * early if the phase hasn't been started yet, is already completed, or is already
+ * emitted). This lets the effect safely re-fire on every databaseTreeNodes change
+ * until the phase has actually been started via startPhase() in Explorer.tsx.
  */
 export function useDatabaseLoadScenario(databaseTreeNodes: unknown[], fetchSucceeded: boolean) {
-  const hasCompletedTreeRenderRef = React.useRef(false);
-
   // Track DatabaseTreeRendered phase (only if fetch succeeded)
   React.useEffect(() => {
-    if (!hasCompletedTreeRenderRef.current && fetchSucceeded) {
-      hasCompletedTreeRenderRef.current = true;
+    if (fetchSucceeded) {
       scenarioMonitor.completePhase(MetricScenario.DatabaseLoad, ApplicationMetricPhase.DatabaseTreeRendered);
     }
   }, [databaseTreeNodes, fetchSucceeded]);