feat(web): improve web build configuration and accessibility

- Add source maps and web renderer build arguments with defaults
- Configure Caddy with CSP headers, cache policies, and service worker handling
- Defer loading of import screen for performance optimization
- Add semantic labels to icons for accessibility
- Update web index.html with Swedish language, meta tags, and description
- Add robots.txt and lighthouse configuration
- Add new planning documents and archive entries

flutter/lib/core/ui/app_shell.dart

@@ -181,9 +181,14 @@ class AppShell extends ConsumerWidget {
                       tooltip: view.mode == RecipesViewMode.grid
                           ? 'Visa som lista'
                           : 'Visa som grid',
-                      icon: Icon(view.mode == RecipesViewMode.grid
-                          ? Icons.view_list
-                          : Icons.grid_view),
+                      icon: Icon(
+                        view.mode == RecipesViewMode.grid
+                            ? Icons.view_list
+                            : Icons.grid_view,
+                        semanticLabel: view.mode == RecipesViewMode.grid
+                            ? 'Visa som lista'
+                            : 'Visa som grid',
+                      ),
                       onPressed: () =>
                           ref.read(recipesViewProvider.notifier).toggleMode(),
                     ),
@@ -207,7 +212,10 @@ class AppShell extends ConsumerWidget {
             ),
           PopupMenuButton<String>(
             tooltip: 'Profil och konto',
-            icon: const Icon(Icons.account_circle_outlined),
+            icon: const Icon(
+              Icons.account_circle_outlined,
+              semanticLabel: 'Profil och konto',
+            ),
             onSelected: (value) async {
               switch (value) {
                 case 'profile':