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/views/ClaimView.vue

@@ -578,8 +578,7 @@ export default class ClaimView extends Vue {
   libsUtil = libsUtil;
   serverUtil = serverUtil;
 
-  // Add notification helpers
-  private notify = createNotifyHelpers(this.$notify);
+  notify!: ReturnType<typeof createNotifyHelpers>;
 
   // =================================================
   // COMPUTED PROPERTIES
@@ -746,6 +745,8 @@ export default class ClaimView extends Vue {
     this.windowDeepLink = `${APP_SERVER}/deep-link/claim/${claimId}`;
 
     this.canShare = !!navigator.share;
+
+    this.notify = createNotifyHelpers(this.$notify);
   }
 
   // insert a space before any capital letters except the initial letter