feat: Refactor routing and navigation structure with StatefulShellRoute

- Introduced a new function `_shellBranchIndexForPath` to determine the index of the shell branch based on the path.
- Replaced `ShellRoute` with `StatefulShellRoute.indexedStack` for better state management during navigation.
- Updated `AppShell` to handle navigation path changes and integrate with the new routing structure.
- Organized routes into `StatefulShellBranch` for better modularity and clarity.
- Enhanced admin panel functionality with improved alias management and UI updates.
- Added new methods in `ReceiptImportSessionNotifier` for managing selected items and edits more efficiently.
- Improved UI components in receipt import and admin panels for better performance and user experience.
- Added PageStorageKeys to various ListViews to maintain scroll positions across navigation.
- Documented performance goals and profiling strategies in a new PERFORMANCE.md file.

flutter/lib/features/inventory/presentation/inventory_screen.dart

@@ -99,6 +99,7 @@ class InventoryScreen extends ConsumerWidget {
           return Stack(
             children: [
               ListView(
+                key: const PageStorageKey<String>('inventory-empty-list'),
                 padding: const EdgeInsets.only(bottom: 88),
                 children: [
                   filterSection,
@@ -109,6 +110,7 @@ class InventoryScreen extends ConsumerWidget {
                 right: 16,
                 bottom: 16,
                 child: FloatingActionButton.extended(
+                  heroTag: 'inventory_add_empty',
                   onPressed: () => context.push('/inventory/create'),
                   icon: const Icon(Icons.add),
                   label: Text(context.l10n.addAction),
@@ -120,6 +122,7 @@ class InventoryScreen extends ConsumerWidget {
         return Stack(
           children: [
             ListView.separated(
+              key: const PageStorageKey<String>('inventory-main-list'),
               padding: const EdgeInsets.only(bottom: 88),
               itemCount: visibleItems.length + 1,
               separatorBuilder: (_, __) => const Divider(height: 1),
@@ -136,12 +139,14 @@ class InventoryScreen extends ConsumerWidget {
                 mainAxisSize: MainAxisSize.min,
                 children: [
                   FloatingActionButton.extended(
+                    heroTag: 'inventory_add',
                     onPressed: () => context.push('/inventory/create'),
                     icon: const Icon(Icons.add),
                     label: Text(context.l10n.addAction),
                   ),
                   const SizedBox(height: 8),
                   FloatingActionButton.extended(
+                    heroTag: 'inventory_go_recipes',
                     onPressed: () => context.go('/recipes'),
                     icon: const Icon(Icons.restaurant_menu),
                     label: Text(context.l10n.inventoryRecipesAction),