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/DesktopModeChooser.css

@@ -0,0 +1,30 @@
+.desktop-mode-chooser {
+  max-width: 640px;
+  margin: 0 auto;
+  padding: var(--space-2xl);
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-lg);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-lg);
+  background: var(--card);
+  box-shadow: var(--shadow-md);
+}
+
+.desktop-mode-chooser__title {
+  margin: 0;
+  font-size: 1.5rem;
+  line-height: 1.2;
+  color: var(--text);
+}
+
+.desktop-mode-chooser__subtitle {
+  margin: 0;
+  color: var(--text-muted);
+}
+
+.desktop-mode-chooser__actions {
+  display: flex;
+  gap: var(--space-md);
+  flex-wrap: wrap;
+}

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

@@ -0,0 +1,48 @@
+import React, { useState } from "react";
+import "./DesktopModeChooser.css";
+
+export type DesktopModeChoice = "local" | "remote";
+
+interface DesktopModeChooserProps {
+  onSelectMode: (mode: DesktopModeChoice) => Promise<void>;
+}
+
+export function DesktopModeChooser({ onSelectMode }: DesktopModeChooserProps) {
+  const [pendingMode, setPendingMode] = useState<DesktopModeChoice | null>(null);
+
+  const handleSelect = async (mode: DesktopModeChoice) => {
+    setPendingMode(mode);
+    try {
+      await onSelectMode(mode);
+    } finally {
+      setPendingMode(null);
+    }
+  };
+
+  return (
+    <section className="desktop-mode-chooser" data-testid="desktop-mode-chooser">
+      <h1 className="desktop-mode-chooser__title">How do you want to run Fusion?</h1>
+      <p className="desktop-mode-chooser__subtitle">
+        Run Fusion locally in this app, or continue with remote server setup.
+      </p>
+      <div className="desktop-mode-chooser__actions">
+        <button
+          type="button"
+          className="btn btn-primary"
+          onClick={() => void handleSelect("local")}
+          disabled={pendingMode !== null}
+        >
+          Continue with Local Fusion
+        </button>
+        <button
+          type="button"
+          className="btn"
+          onClick={() => void handleSelect("remote")}
+          disabled={pendingMode !== null}
+        >
+          Continue to Remote Connection
+        </button>
+      </div>
+    </section>
+  );
+}

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>
+  );
+}