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

compose.flutter.yml

@@ -3,8 +3,10 @@ services:
     build:
       context: ./flutter
       dockerfile: Dockerfile
-      args:
-        API_BASE_URL: "/api"
+      args:
+        API_BASE_URL: "/api"
+        SOURCE_MAPS: "false"
+        WEB_RENDERER: "auto"
     image: recipe-flutter:local
     container_name: recipe-flutter
     restart: unless-stopped