feat(FN-1076): integrate desktop IPC bridge and lifecycle modules

- Extract main-process IPC registration into src/ipc.ts for window controls, system info, tray status, updater checks, and native dialogs
- Refactor main.ts startup into initializeApp/run and wire menu, tray, deep-link, updater, and window-state restore/quit cleanup
- Rework preload bridge to expose typed window.fusionAPI subscriptions and replace preload.d.ts with shared src/types.d.ts global declarations
- Add comprehensive tests for IPC handlers, preload contracts, and main-process integration behavior
- Document IPC channels, preload API, and lifecycle sequencing in packages/desktop/README.md

packages/desktop/src/ipc.ts

@@ -0,0 +1,53 @@
+import { app, type BrowserWindow, ipcMain, type Tray } from "electron";
+import { setupAutoUpdater, showExportSettingsDialog, showImportSettingsDialog } from "./native.js";
+import { type EngineStatus, updateTrayStatus } from "./tray.js";
+
+export function registerIpcHandlers(mainWindow: BrowserWindow, tray: Tray): void {
+  ipcMain.handle("window:minimize", () => {
+    mainWindow.minimize();
+  });
+
+  ipcMain.handle("window:maximize", () => {
+    const isCurrentlyMaximized = mainWindow.isMaximized();
+    if (isCurrentlyMaximized) {
+      mainWindow.unmaximize();
+      return false;
+    }
+
+    mainWindow.maximize();
+    return true;
+  });
+
+  ipcMain.handle("window:close", () => {
+    mainWindow.close();
+  });
+
+  ipcMain.handle("window:isMaximized", () => mainWindow.isMaximized());
+
+  ipcMain.handle("app:getSystemInfo", () => ({
+    platform: process.platform,
+    arch: process.arch,
+    electronVersion: process.versions.electron,
+    nodeVersion: process.versions.node,
+    appVersion: app.getVersion(),
+  }));
+
+  ipcMain.handle("app:checkForUpdates", () => {
+    try {
+      setupAutoUpdater(mainWindow);
+      return { status: "checking" as const };
+    } catch (error) {
+      return {
+        status: "error" as const,
+        error: error instanceof Error ? error.message : String(error),
+      };
+    }
+  });
+
+  ipcMain.handle("tray:updateStatus", (_event, status: EngineStatus) => {
+    updateTrayStatus(tray, status);
+  });
+
+  ipcMain.handle("native:showExportDialog", () => showExportSettingsDialog(mainWindow));
+  ipcMain.handle("native:showImportDialog", () => showImportSettingsDialog(mainWindow));
+}