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/pantry/presentation/pantry_screen.dart

@@ -325,6 +325,7 @@ class _PantryScreenState extends ConsumerState<PantryScreen> {
 
     final content = filteredItems.isEmpty
         ? ListView(
+            key: const PageStorageKey<String>('pantry-empty-list'),
             padding: const EdgeInsets.fromLTRB(12, 0, 12, 96),
             children: [
               filterSection,
@@ -335,6 +336,7 @@ class _PantryScreenState extends ConsumerState<PantryScreen> {
             ],
           )
         : ListView.separated(
+          key: const PageStorageKey<String>('pantry-main-list'),
             padding: const EdgeInsets.fromLTRB(12, 0, 12, 96),
             itemCount: filteredItems.length + 1,
             separatorBuilder: (_, __) => const Divider(height: 1),
@@ -384,12 +386,14 @@ class _PantryScreenState extends ConsumerState<PantryScreen> {
             mainAxisSize: MainAxisSize.min,
             children: [
               FloatingActionButton.extended(
+                heroTag: 'pantry_add',
                 onPressed: () => context.push('/inventory/create?destination=pantry'),
                 icon: const Icon(Icons.add),
                 label: Text(context.l10n.addAction),
               ),
               const SizedBox(height: 8),
               FloatingActionButton.extended(
+                heroTag: 'pantry_go_recipes',
                 onPressed: () => context.go('/recipes'),
                 icon: const Icon(Icons.restaurant_menu),
                 label: Text(context.l10n.inventoryRecipesAction),