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/import/data/receipt_import_session.dart

@@ -186,6 +186,20 @@ class ReceiptImportSessionNotifier
     unawaited(_persist());
   }
 
+  void setImportedResult({
+    required List<ParsedReceiptItem> items,
+    required Map<int, ItemEdit> edits,
+    required Map<int, bool> selected,
+  }) {
+    final current = state ?? const ReceiptImportSession();
+    state = current.copyWith(
+      items: items,
+      edits: edits,
+      selected: selected,
+    );
+    unawaited(_persist());
+  }
+
   void setEdit(int index, ItemEdit edit) {
     if (state == null) return;
     final edits = Map<int, ItemEdit>.from(state!.edits)..[index] = edit;
@@ -200,6 +214,25 @@ class ReceiptImportSessionNotifier
     unawaited(_persist());
   }
 
+  void setSelectedForIndexes(Iterable<int> indexes, bool value) {
+    if (state == null) return;
+    final selected = Map<int, bool>.from(state!.selected);
+    for (final index in indexes) {
+      selected[index] = value;
+    }
+    state = state!.copyWith(selected: selected);
+    unawaited(_persist());
+  }
+
+  void setSelectedForAll(int count, bool value) {
+    if (state == null) return;
+    final selected = <int, bool>{
+      for (var i = 0; i < count; i++) i: value,
+    };
+    state = state!.copyWith(selected: selected);
+    unawaited(_persist());
+  }
+
   Future<void> restore() async {
     final prefs = await SharedPreferences.getInstance();
     final raw = prefs.getString(_storageKey);