feat(FN-3399): route desktop remote mode into shell onboarding flow

Removes the standalone `DesktopShellBootstrap` component from the desktop package, routing desktop remote mode into the shell onboarding flow instead. Updates the corresponding test file to reflect the component removal and adjusts the README.

Fusion-Task-Id: FN-3399

packages/desktop/src/renderer/components/DesktopShellBootstrap.tsx

@@ -0,0 +1,78 @@
+import React, { useEffect, useMemo, useState } from "react";
+import { DesktopWrapper } from "./DesktopWrapper";
+import { DesktopModeChooser, type DesktopModeChoice } from "./DesktopModeChooser";
+
+interface DesktopModeState {
+  isFirstRun: boolean;
+  desktopMode: DesktopModeChoice | null;
+}
+
+interface FusionShellWithModeApi {
+  getDesktopModeState: () => Promise<DesktopModeState>;
+  setDesktopMode: (mode: DesktopModeChoice) => Promise<unknown>;
+}
+
+function getFusionShell(): FusionShellWithModeApi | null {
+  if (typeof window === "undefined") {
+    return null;
+  }
+
+  const api = (window as Window & { fusionShell?: Partial<FusionShellWithModeApi> }).fusionShell;
+  if (!api?.getDesktopModeState || !api?.setDesktopMode) {
+    return null;
+  }
+
+  return api as FusionShellWithModeApi;
+}
+
+export function DesktopShellBootstrap({ DashboardApp }: { DashboardApp: React.ComponentType }) {
+  const fusionShell = useMemo(() => getFusionShell(), []);
+  const [modeState, setModeState] = useState<DesktopModeState | null>(null);
+
+  useEffect(() => {
+    if (!fusionShell) {
+      setModeState({ isFirstRun: false, desktopMode: "local" });
+      return;
+    }
+
+    let cancelled = false;
+    void fusionShell.getDesktopModeState().then((state) => {
+      if (!cancelled) {
+        setModeState(state);
+      }
+    }).catch(() => {
+      if (!cancelled) {
+        setModeState({ isFirstRun: false, desktopMode: "local" });
+      }
+    });
+
+    return () => {
+      cancelled = true;
+    };
+  }, [fusionShell]);
+
+  const handleModeSelect = async (mode: DesktopModeChoice) => {
+    if (fusionShell) {
+      await fusionShell.setDesktopMode(mode);
+    }
+    setModeState({ isFirstRun: false, desktopMode: mode });
+  };
+
+  if (!modeState) {
+    return null;
+  }
+
+  if (modeState.isFirstRun) {
+    return (
+      <DesktopWrapper>
+        <DesktopModeChooser onSelectMode={handleModeSelect} />
+      </DesktopWrapper>
+    );
+  }
+
+  return (
+    <DesktopWrapper>
+      <DashboardApp />
+    </DesktopWrapper>
+  );
+}