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/admin/presentation/admin_aliases_panel.dart

@@ -166,6 +166,49 @@ class _AdminAliasesPanelState extends ConsumerState<AdminAliasesPanel> {
           alias.displayProductName.toLowerCase().contains(query);
     }).toList();
 
+    Widget buildAliasCard(ReceiptAlias alias) {
+      return Card(
+        child: ListTile(
+          leading: const Icon(Icons.link_outlined),
+          title: Text(alias.receiptName, style: const TextStyle(fontWeight: FontWeight.w500)),
+          subtitle: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            mainAxisSize: MainAxisSize.min,
+            children: [
+              Text(
+                '→ ${alias.displayProductName}',
+                style: const TextStyle(fontWeight: FontWeight.w400),
+              ),
+              Text(
+                'Produkt-ID: ${alias.productId}',
+                style: TextStyle(
+                  fontSize: 11,
+                  color: Theme.of(context).colorScheme.outline,
+                ),
+              ),
+            ],
+          ),
+          trailing: IconButton(
+            onPressed: () => _removeAlias(alias),
+            icon: const Icon(Icons.delete_outline),
+            tooltip: 'Ta bort alias',
+            color: Theme.of(context).colorScheme.error,
+          ),
+        ),
+      );
+    }
+
+    Widget buildAliasList({EdgeInsetsGeometry padding = EdgeInsets.zero}) {
+      return ListView.builder(
+        padding: padding,
+        itemCount: filteredAliases.length,
+        itemBuilder: (context, index) {
+          final alias = filteredAliases[index];
+          return buildAliasCard(alias);
+        },
+      );
+    }
+
     final content = Column(
       crossAxisAlignment: CrossAxisAlignment.start,
       children: [
@@ -230,51 +273,37 @@ class _AdminAliasesPanelState extends ConsumerState<AdminAliasesPanel> {
           onChanged: (value) => setState(() => _search = value),
         ),
         const SizedBox(height: 12),
-        if (filteredAliases.isEmpty)
-          const Text('Inga alias hittades.')
-        else
-          ...filteredAliases.map(
-            (alias) => Card(
-              child: ListTile(
-                leading: const Icon(Icons.link_outlined),
-                title: Text(alias.receiptName, style: const TextStyle(fontWeight: FontWeight.w500)),
-                subtitle: Column(
-                  crossAxisAlignment: CrossAxisAlignment.start,
-                  mainAxisSize: MainAxisSize.min,
-                  children: [
-                    Text(
-                      '→ ${alias.displayProductName}',
-                      style: const TextStyle(fontWeight: FontWeight.w400),
-                    ),
-                    Text(
-                      'Produkt-ID: ${alias.productId}',
-                      style: TextStyle(
-                        fontSize: 11,
-                        color: Theme.of(context).colorScheme.outline,
-                      ),
-                    ),
-                  ],
-                ),
-                trailing: IconButton(
-                  onPressed: () => _removeAlias(alias),
-                  icon: const Icon(Icons.delete_outline),
-                  tooltip: 'Ta bort alias',
-                  color: Theme.of(context).colorScheme.error,
-                ),
-              ),
-            ),
-          ),
+        if (filteredAliases.isEmpty) const Text('Inga alias hittades.'),
       ],
     );
 
     if (!widget.embedded) {
+      if (filteredAliases.isEmpty) {
+        return ListView(
+          padding: const EdgeInsets.all(16),
+          children: [content],
+        );
+      }
       return ListView(
         padding: const EdgeInsets.all(16),
-        children: [content],
+        children: [
+          content,
+          const SizedBox(height: 8),
+          ...filteredAliases.map(buildAliasCard),
+        ],
       );
     }
 
-    return content;
+    if (filteredAliases.isEmpty) return content;
+
+    return Column(
+      crossAxisAlignment: CrossAxisAlignment.start,
+      children: [
+        content,
+        const SizedBox(height: 8),
+        Expanded(child: buildAliasList()),
+      ],
+    );
   }
 }