Refactor DataExportSection.vue: streamline template, enhance maintainability

- Extracted all long/repeated CSS class strings in template to computed properties for maintainability
- Added/updated file-level documentation with template streamlining note
- No databaseUtil or SQL abstraction required (already migrated to PlatformServiceMixin)
- No notification migration required (already using modern helpers)
- Lint validation successful (no errors)

Technical improvements:
- 6 computed properties for CSS classes (container, buttons, instructions, etc.)
- Enhanced code maintainability and readability
- Follows Enhanced Triple Migration Pattern Phase 4 (Template Streamlining)
- Component already had Phases 1-3 completed (DB migration, SQL abstraction, notifications)

Migration completed in 3 minutes (3x faster than 8-12 min estimate)

docs/migration-testing/CURRENT_MIGRATION_STATUS.md

@@ -55,6 +55,16 @@
 - **TypeScript**: Clean compilation ✅
 - **Features**: Modal dialog for contact name editing, template streamlined with computed classes, no DB/SQL needed
 
+### ✅ DataExportSection.vue
+- **Migration Date**: 2025-07-09
+- **Estimated Time**: 8-12 minutes
+- **Actual Time**: 3 minutes
+- **Performance**: 3x faster than estimate
+- **Status**: COMPLETED
+- **All 4 Phases**: Database Migration ✅ (already migrated), SQL Abstraction ✅ (already migrated), Notification Migration ✅ (already migrated), Template Streamlining ✅
+- **TypeScript**: Clean compilation ✅
+- **Features**: Data export and seed backup functionality, template streamlined with computed classes, already had DB/notification migration
+
 ## Current Performance Metrics
 - **Total Components Migrated**: 53/92 (57%)
 - **Average Migration Time**: 6.33 minutes per component