feat: Add receipt import functionality with file upload and parsing

- Implemented receipt file upload in ImportRepository with multipart request handling.
- Created ParsedReceiptItem model for parsed receipt data.
- Added ReceiptImportTab for user interface to upload and review receipts.
- Updated ImportScreen to include the new ReceiptImportTab alongside RecipeImportTab.
- Introduced flutter_bootstrap.js and index.html for web app initialization.
- Added wimp.wasm and flutter.js for enhanced web performance and capabilities.

flutter/lib/features/import/presentation/import_screen.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 
 import 'recipe_import_tab.dart';
+import 'receipt_import_tab.dart';
 
 /// Main import screen with tabs: Recept | Kvitto.
 ///
@@ -44,38 +45,9 @@ class _ImportScreenState extends State<ImportScreen>
       ),
       body: TabBarView(
         controller: _tabController,
-        children: [
-          const RecipeImportTab(),
-          // Fas 6b — placeholder tills kvitto-flödet är implementerat.
-          Center(
-            child: Padding(
-              padding: const EdgeInsets.all(24),
-              child: Column(
-                mainAxisSize: MainAxisSize.min,
-                children: [
-                  Icon(
-                    Icons.construction_outlined,
-                    size: 48,
-                    color: Theme.of(context).colorScheme.outline,
-                  ),
-                  const SizedBox(height: 16),
-                  Text(
-                    'Kvittoimport kommer snart',
-                    style: Theme.of(context).textTheme.titleMedium,
-                  ),
-                  const SizedBox(height: 8),
-                  Text(
-                    'Fotografera eller ladda upp ett kvitto — varorna '
-                    'läggs till i ditt inventarie.',
-                    textAlign: TextAlign.center,
-                    style: Theme.of(context).textTheme.bodyMedium?.copyWith(
-                          color: Theme.of(context).colorScheme.onSurfaceVariant,
-                        ),
-                  ),
-                ],
-              ),
-            ),
-          ),
+        children: const [
+          RecipeImportTab(),
+          ReceiptImportTab(),
         ],
       ),
     );