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/MetricScenarioConfigs.ts

@@ -5,16 +5,10 @@ export const scenarioConfigs: Record<MetricScenario, ScenarioConfig> = {
   [MetricScenario.ApplicationLoad]: {
     requiredPhases: [
       ApplicationMetricPhase.PlatformConfigured,
-      ApplicationMetricPhase.CopilotConfigured,
-      ApplicationMetricPhase.SampleDataLoaded,
       ApplicationMetricPhase.ExplorerInitialized,
       CommonMetricPhase.Interactive,
     ],
-    deferredPhases: [
-      ApplicationMetricPhase.CopilotConfigured,
-      ApplicationMetricPhase.SampleDataLoaded,
-      ApplicationMetricPhase.ExplorerInitialized,
-    ],
+    deferredPhases: [ApplicationMetricPhase.ExplorerInitialized],
     timeoutMs: 10000,
   },
   [MetricScenario.DatabaseLoad]: {