refactor: standardize notify helper usage and document migration workflow

- Refactor notify usage in GiftedDialog.vue, AccountViewView.vue, ClaimView.vue, and DataExportSection.vue:
  • Use notify as a property initialized in created() with createNotifyHelpers(this.$notify)
  • Remove getter-based notify patterns for consistency and lifecycle safety
  • Fix linter/type errors related to notify property initialization

- Add mandatory per-file migration workflow to doc/migration-progress-tracker.md:
  • For each file: (1) migrate to PlatformServiceMixin, (2) immediately standardize notify usage and fix linter/type errors
  • Clarifies this two-step process is required for every file, not as a global sweep

All migrated files are now consistent, maintainable, and ready for further migration work.

src/components/DataExportSection.vue

@@ -98,9 +98,7 @@ export default class DataExportSection extends Vue {
    * Notification helper for consistent notification patterns
    * Created as a getter to ensure $notify is available when called
    */
-  get notify() {
-    return createNotifyHelpers(this.$notify);
-  }
+  notify!: ReturnType<typeof createNotifyHelpers>;
 
   /**
    * NOTE: PlatformServiceMixin provides both concise helpers (e.g. $contacts, capabilities)
@@ -156,5 +154,9 @@ export default class DataExportSection extends Vue {
       this.isExporting = false;
     }
   }
+
+  created() {
+    this.notify = createNotifyHelpers(this.$notify);
+  }
 }
 </script>