feat(FN-3398): update desktop README with multi-project setup and troublesh

The merge lands Step 7 of FN-3398, adding documentation and delivery artifacts across the mobile and desktop packages with updated READMEs, mobile-specific docs, and architecture references.

Fusion-Task-Id: FN-3398

packages/desktop/src/shell-settings.ts

@@ -0,0 +1,58 @@
+import { readFile, rename, writeFile } from "node:fs/promises";
+import { join } from "node:path";
+import { app } from "electron";
+
+export interface ShellConnectionProfile {
+  id: string;
+  name: string;
+  serverUrl: string;
+  authToken?: string | null;
+  createdAt: string;
+  updatedAt: string;
+  lastUsedAt?: string | null;
+}
+
+export interface DesktopShellSettings {
+  desktopMode: "local" | "remote";
+  activeProfileId: string | null;
+  profiles: ShellConnectionProfile[];
+}
+
+const DEFAULT_SETTINGS: DesktopShellSettings = {
+  desktopMode: "remote",
+  activeProfileId: null,
+  profiles: [],
+};
+
+function getSettingsPath(): string {
+  return join(app.getPath("userData"), "shell-connections.json");
+}
+
+function normalize(input: unknown): DesktopShellSettings {
+  if (!input || typeof input !== "object") {
+    return { ...DEFAULT_SETTINGS };
+  }
+
+  const candidate = input as Partial<DesktopShellSettings>;
+  return {
+    desktopMode: candidate.desktopMode === "local" ? "local" : "remote",
+    activeProfileId: typeof candidate.activeProfileId === "string" ? candidate.activeProfileId : null,
+    profiles: Array.isArray(candidate.profiles) ? candidate.profiles.filter((item) => item && typeof item === "object") as ShellConnectionProfile[] : [],
+  };
+}
+
+export async function readShellSettings(): Promise<DesktopShellSettings> {
+  try {
+    const raw = await readFile(getSettingsPath(), "utf-8");
+    return normalize(JSON.parse(raw));
+  } catch {
+    return { ...DEFAULT_SETTINGS };
+  }
+}
+
+export async function writeShellSettings(settings: DesktopShellSettings): Promise<void> {
+  const path = getSettingsPath();
+  const temp = `${path}.tmp`;
+  await writeFile(temp, JSON.stringify(settings, null, 2), "utf-8");
+  await rename(temp, path);
+}