feat: implement secure IPC-based file export for Electron

Replace sandboxed Capacitor filesystem with native IPC for reliable file exports:
- Add IPC handler in main process for direct Downloads folder access
- Expose secure electronAPI via contextBridge in preload script
- Update ElectronPlatformService to use native IPC with web fallback
- Add TypeScript definitions for electron APIs
- Fix file export issues where files were trapped in virtual filesystem
- Enable proper date-stamped backup filenames in Downloads folder
- Follow Electron security best practices with process isolation

Files now export directly to ~/Downloads with exact path feedback.

src/services/PlatformServiceFactory.ts

@@ -1,6 +1,7 @@
 import { PlatformService } from "./PlatformService";
 import { WebPlatformService } from "./platforms/WebPlatformService";
 import { CapacitorPlatformService } from "./platforms/CapacitorPlatformService";
+import { ElectronPlatformService } from "./platforms/ElectronPlatformService";
 
 /**
  * Factory class for creating platform-specific service implementations.
@@ -76,56 +77,3 @@ export class PlatformServiceFactory {
     };
   }
 }
-
-/**
- * Electron-specific platform service implementation.
- * Extends CapacitorPlatformService with electron-specific overrides.
- *
- * This service handles the unique requirements of the Electron platform:
- * - Desktop-specific capabilities
- * - Electron-specific file system access
- * - Desktop UI patterns
- * - Native desktop integration
- */
-class ElectronPlatformService extends CapacitorPlatformService {
-  /**
-   * Gets the capabilities of the Electron platform
-   * Overrides the mobile-focused capabilities from CapacitorPlatformService
-   * @returns Platform capabilities object specific to Electron
-   */
-  getCapabilities() {
-    return {
-      hasFileSystem: true,
-      hasCamera: false, // Desktop typically doesn't have integrated cameras for our use case
-      isMobile: false, // Electron is desktop, not mobile
-      isIOS: false,
-      hasFileDownload: true, // Desktop supports direct file downloads
-      needsFileHandlingInstructions: false, // Desktop users are familiar with file handling
-      isNativeApp: true, // Electron is a native app
-    };
-  }
-
-  /**
-   * Checks if running on Electron platform.
-   * @returns true, as this is the Electron implementation
-   */
-  isElectron(): boolean {
-    return true;
-  }
-
-  /**
-   * Checks if running on Capacitor platform.
-   * @returns false, as this is Electron, not pure Capacitor
-   */
-  isCapacitor(): boolean {
-    return false;
-  }
-
-  /**
-   * Checks if running on web platform.
-   * @returns false, as this is not web
-   */
-  isWeb(): boolean {
-    return false;
-  }
-}