feat: Improve database export with native sharing on mobile

- Enhance CapacitorPlatformService to use native share sheet via Web Share API
- Add fallback to Capacitor Share API with temporary file storage
- Implement WebPlatformService export with direct download for desktop
- Clean up temporary files and URLs after sharing/download

The changes provide a more platform-appropriate experience:
- Mobile: Uses system share sheet for flexible saving/sharing options
- Desktop: Direct download to user's download folder

src/components/DataExportSection.vue

@@ -139,22 +139,7 @@ export default class DataExportSection extends Vue {
       const blob = await db.export({ prettyJson: true });
       const fileName = `${db.name}-backup.json`;
 
-      if (this.platformService.isWeb()) {
-        // Web platform: Use download link
-        this.downloadUrl = URL.createObjectURL(blob);
-        const downloadAnchor = this.$refs.downloadLink as HTMLAnchorElement;
-        downloadAnchor.href = this.downloadUrl;
-        downloadAnchor.download = fileName;
-        downloadAnchor.click();
-        setTimeout(() => URL.revokeObjectURL(this.downloadUrl), 1000);
-      } else if (this.platformService.isCapacitor()) {
-        // Capacitor platform: Write to app directory
-        const content = await blob.text();
-        await this.platformService.writeFile(fileName, content);
-      } else {
-        // Other platforms: Use platform service
-        await this.platformService.writeFile(fileName, await blob.text());
-      }
+      await this.platformService.exportDatabase(blob, fileName);
 
       this.$notify(
         {

src/services/PlatformService.ts

@@ -46,6 +46,15 @@ export interface PlatformService {
    */
   listFiles(directory: string): Promise<string[]>;
 
+  /**
+   * Exports a database blob to a file, handling platform-specific save operations.
+   * @param blob - The database blob to export
+   * @param fileName - The name of the file to save
+   * @returns Promise that resolves when the export is complete
+   * @throws Error if export fails
+   */
+  exportDatabase(blob: Blob, fileName: string): Promise<void>;
+
   // Camera operations
   /**
    * Activates the device camera to take a picture.

src/services/platforms/CapacitorPlatformService.ts

@@ -2,6 +2,7 @@ import { ImageResult, PlatformService } from "../PlatformService";
 import { Filesystem, Directory } from "@capacitor/filesystem";
 import { Camera, CameraResultType, CameraSource } from "@capacitor/camera";
 import { logger } from "../../utils/logger";
+import { Share } from "@capacitor/share";
 
 /**
  * Platform service implementation for Capacitor (mobile) platform.
@@ -188,4 +189,55 @@ export class CapacitorPlatformService implements PlatformService {
     // This is just a placeholder for the interface
     return Promise.resolve();
   }
+
+  async exportDatabase(blob: Blob, fileName: string): Promise<void> {
+    // Create a File object from the Blob
+    const file = new File([blob], fileName, { type: 'application/json' });
+    
+    try {
+      // Use the native share sheet
+      await navigator.share({
+        files: [file],
+        title: fileName,
+      });
+    } catch (error) {
+      // Fallback to Capacitor Share API if Web Share API fails
+      // First save to temporary file
+      const base64Data = await this.blobToBase64(blob);
+      const result = await Filesystem.writeFile({
+        path: fileName,
+        data: base64Data,
+        directory: Directory.Cache, // Use Cache instead of Documents for temporary files
+        recursive: true
+      });
+      
+      // Then share using Capacitor Share API
+      await Share.share({
+        title: fileName,
+        url: result.uri
+      });
+      
+      // Clean up the temporary file
+      try {
+        await Filesystem.deleteFile({
+          path: fileName,
+          directory: Directory.Cache
+        });
+      } catch (cleanupError) {
+        logger.warn('Failed to clean up temporary file:', cleanupError);
+      }
+    }
+  }
+
+  private async blobToBase64(blob: Blob): Promise<string> {
+    return new Promise((resolve, reject) => {
+      const reader = new FileReader();
+      reader.onloadend = () => {
+        const base64data = reader.result as string;
+        resolve(base64data.split(',')[1]);
+      };
+      reader.onerror = reject;
+      reader.readAsDataURL(blob);
+    });
+  }
 }

src/services/platforms/WebPlatformService.ts

@@ -209,4 +209,13 @@ export class WebPlatformService implements PlatformService {
     // Web platform can handle deep links through URL parameters
     return Promise.resolve();
   }
+
+  async exportDatabase(blob: Blob, fileName: string): Promise<void> {
+    const downloadUrl = URL.createObjectURL(blob);
+    const downloadAnchor = document.createElement('a');
+    downloadAnchor.href = downloadUrl;
+    downloadAnchor.download = fileName;
+    downloadAnchor.click();
+    setTimeout(() => URL.revokeObjectURL(downloadUrl), 1000);
+  }
 }