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/Platform/Hosted/extractFeatures.ts

@@ -31,11 +31,6 @@ export type Features = {
   readonly mongoProxyAPIs?: string;
   readonly enableThroughputCap: boolean;
   readonly enableHierarchicalKeys: boolean;
-  readonly enableCopilot: boolean;
-  readonly copilotVersion?: string;
-  readonly disableCopilotPhoenixGateaway: boolean;
-  readonly enableCopilotFullSchema: boolean;
-  readonly copilotChatFixedMonacoEditorHeight: boolean;
   readonly enablePriorityBasedExecution: boolean;
   readonly disableConnectionStringLogin: boolean;
   readonly enableContainerCopy: boolean;
@@ -104,11 +99,6 @@ export function extractFeatures(given = new URLSearchParams(window.location.sear
     notebooksDownBanner: "true" === get("notebooksDownBanner"),
     enableThroughputCap: "true" === get("enablethroughputcap"),
     enableHierarchicalKeys: "true" === get("enablehierarchicalkeys"),
-    enableCopilot: "true" === get("enablecopilot", "true"),
-    copilotVersion: get("copilotversion") ?? "v2.0",
-    disableCopilotPhoenixGateaway: "true" === get("disablecopilotphoenixgateaway"),
-    enableCopilotFullSchema: "true" === get("enablecopilotfullschema", "true"),
-    copilotChatFixedMonacoEditorHeight: "true" === get("copilotchatfixedmonacoeditorheight"),
     enablePriorityBasedExecution: "true" === get("enableprioritybasedexecution"),
     disableConnectionStringLogin: "true" === get("disableconnectionstringlogin"),
     enableContainerCopy: "true" === get("enablecontainercopy"),