refactor(platform): replace platform checks with capability-based system

- Add PlatformCapabilities interface to define available features
- Remove isWeb(), isCapacitor(), isElectron(), isPyWebView() methods
- Update platform services to implement getCapabilities()
- Refactor DataExportSection to use capability checks instead of platform checks
- Improve platform abstraction and separation of concerns
- Make platform-specific logic more maintainable and extensible

This change decouples components from specific platform implementations,
making the codebase more maintainable and easier to extend with new platforms.

src/components/DataExportSection.vue

@@ -42,17 +42,17 @@
     >
       If no download happened yet, click again here to download now.
     </a>
-    <div class="mt-4" v-if="showPlatformInstructions">
+    <div class="mt-4" v-if="platformCapabilities.needsFileHandlingInstructions">
       <p>
         After the download, you can save the file in your preferred storage
         location.
       </p>
       <ul>
-        <li v-if="platformService.isCapacitor() && isIOS" class="list-disc list-outside ml-4">
+        <li v-if="platformCapabilities.isIOS" class="list-disc list-outside ml-4">
           On iOS: Choose "More..." and select a place in iCloud, or go "Back"
           and save to another location.
         </li>
-        <li v-if="platformService.isCapacitor() && !isIOS" class="list-disc list-outside ml-4">
+        <li v-if="platformCapabilities.isMobile && !platformCapabilities.isIOS" class="list-disc list-outside ml-4">
           On Android: Choose "Open" and then share
           <font-awesome icon="share-nodes" class="fa-fw" />
           to your prefered place.
@@ -68,7 +68,7 @@ import { NotificationIface } from "../constants/app";
 import { db } from "../db/index";
 import { logger } from "../utils/logger";
 import { PlatformServiceFactory } from "../services/PlatformServiceFactory";
-import { PlatformService } from "../services/PlatformService";
+import { PlatformService, PlatformCapabilities } from "../services/PlatformService";
 
 /**
  * @vue-component
@@ -103,17 +103,10 @@ export default class DataExportSection extends Vue {
   private platformService: PlatformService = PlatformServiceFactory.getInstance();
 
   /**
-   * Whether the current platform is iOS
+   * Platform capabilities for the current platform
    */
-  private get isIOS(): boolean {
-    return /iPad|iPhone|iPod/.test(navigator.userAgent);
-  }
-
-  /**
-   * Whether to show platform-specific instructions
-   */
-  private get showPlatformInstructions(): boolean {
-    return this.platformService.isCapacitor();
+  private get platformCapabilities(): PlatformCapabilities {
+    return this.platformService.getCapabilities();
   }
 
   /**
@@ -121,7 +114,7 @@ export default class DataExportSection extends Vue {
    * Revokes object URL when component is unmounted (web platform only)
    */
   beforeUnmount() {
-    if (this.downloadUrl && this.platformService.isWeb()) {
+    if (this.downloadUrl && this.platformCapabilities.hasFileDownload) {
       URL.revokeObjectURL(this.downloadUrl);
     }
   }
@@ -139,7 +132,7 @@ export default class DataExportSection extends Vue {
       const blob = await db.export({ prettyJson: true });
       const fileName = `${db.name}-backup.json`;
 
-      if (this.platformService.isWeb()) {
+      if (this.platformCapabilities.hasFileDownload) {
         // Web platform: Use download link
         this.downloadUrl = URL.createObjectURL(blob);
         const downloadAnchor = this.$refs.downloadLink as HTMLAnchorElement;
@@ -147,13 +140,10 @@ export default class DataExportSection extends Vue {
         downloadAnchor.download = fileName;
         downloadAnchor.click();
         setTimeout(() => URL.revokeObjectURL(this.downloadUrl), 1000);
-      } else if (this.platformService.isCapacitor()) {
-        // Capacitor platform: Write to app directory
+      } else if (this.platformCapabilities.hasFileSystem) {
+        // Native 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());
       }
 
       this.$notify(
@@ -161,7 +151,7 @@ export default class DataExportSection extends Vue {
           group: "alert",
           type: "success",
           title: "Export Successful",
-          text: this.platformService.isWeb()
+          text: this.platformCapabilities.hasFileDownload
             ? "See your downloads directory for the backup. It is in the Dexie format."
             : "The backup has been saved to your device.",
         },
@@ -187,7 +177,7 @@ export default class DataExportSection extends Vue {
    */
   public computedStartDownloadLinkClassNames() {
     return {
-      hidden: this.downloadUrl && this.platformService.isWeb(),
+      hidden: this.downloadUrl && this.platformCapabilities.hasFileDownload,
     };
   }
 
@@ -197,7 +187,7 @@ export default class DataExportSection extends Vue {
    */
   public computedDownloadLinkClassNames() {
     return {
-      hidden: !this.downloadUrl || !this.platformService.isWeb(),
+      hidden: !this.downloadUrl || !this.platformCapabilities.hasFileDownload,
     };
   }
 }